photonic chip equipped with a Mach-Zehnder modulator

Abstract

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

Description

Title of the invention: Photonic chip equipped with a Mach-Zehnder modulator FIELD OF THE INVENTION

[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 (at 3 dB) greater than that of Mach-Zehnder modulators known from the state of the art.

[0003] The photonic chip advantageously comprises an optical transmitter. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0004] Optical modulators are widely implemented in optical transmitters for the manipulation of optical signals. Among the known optical modulators, the Mach-Zehnder type modulator occupies a place of interest when high modulation speeds of light radiation are required.

[0005] Thus, [Fig.l] represents a Mach-Zehnder modulator 1 known from the state of the art. The Mach-Zehnder modulator 1 comprises in particular two modulation branches, called first branch 2 and second branch 3, connected by one of their ends by at least one optical input 4 and by the other of their ends by at least one optical output 5.

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

[0007] The device is also provided with two phase modulators, called first modulator 6 and second modulator 7, intended to impose a phase shift, respectively, on the first radiation and the second radiation before their recombination at the optical output 5. The modification of the phase of one and / or the other of the first and second radiation makes it possible in particular to modulate the intensity of the recombined radiation at the output of the Mach-Zehnder modulator.

[0008] The Mach-Zehnder device also comprises a phase shift means making it possible to impose an additional fixed phase shift q between the first branch 2 and the second branch 3. Conventionally, this fixed phase shift is generally equal to pi / 2 which corresponds to an operating point of the Mach-Zehnder device known as “quadrature” in order to linearize as much as possible the intensity modulation at the output of said device.

[0009] However, the consideration of a quadrature operating point limits the performance of a Mach-Zehnder device.

[0010] Thus, an aim of the present invention is to propose a photonic chip provided with a Mach-Zehnder modulator whose performance is improved compared to Mach-Zehnder devices or transmitters known from the state of the art. BRIEF DESCRIPTION OF THE INVENTION

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

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

[0013] - first means for adjusting the operating point of the modulator of Mach-Zehnder and configured to impose an operating point associated with a fixed phase shift F between one and the other of the first and second branches;

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

[0015] According to one embodiment, the first adjustment means comprise a first heating element configured to locally modify, by heating, the refractive index of one or the other of the first branch and the second branch in order to impose the fixed phase shift F.

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

[0017] According to one embodiment, the first control means comprise a first photodetector and a first spectral analyzer.

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

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

[0020] According to one embodiment, said photonic system comprises second control means configured to control the second adjustment means, said second control means comprising a second photodetector and a second spectral analyzer.

[0021] According to one embodiment, the radiation combiner comprises two output channels called, respectively, first channel and second channel, the second channel carrying the optical amplifier with semiconductor materials, the second control means being carried by a second control waveguide optically coupled to the second channel, the coupling being dimensioned so that the second waveguide takes at most 10%, advantageously at most 5%, of the optical power circulating in the second channel.

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

[0023] According to one embodiment, the photonic chip comprises a laser source configured to inject light radiation at wavelength 1 at an input of the Mach-Zehnder modulator.

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

[0025] The invention also relates to the implementation of the photonic system according to the present invention, in which the light radiation injected by the laser source has an intensity strictly less than 10 dB, advantageously less than 7 dB, and in which the gain of the optical amplifier with semiconductor materials is adjusted so that the signal at the output of the photonic chip has an intensity equivalent to that obtained by said photonic chip without an optical amplifier with semiconductor materials and at the input of which radiation with an intensity of 10 dB would have been injected. Brief description of the drawings

[0026] Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

[0027] [Fig-1] [Fig. 1] is a schematic representation of a Mach Zehnder 1 device known from the state of the art;

[0028] [Fig.2] [Fig.2] is a schematic representation of a Mach-Zehnder modulator capable of being implemented within the framework of the present invention;

[0029] [Fig.3] [Fig.3] is a schematic representation of a support substrate on one face of which the waveguide layer rests, and according to a section plane perpendicular to the front face;

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

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

[0032] [Fig.6] [Fig.6] is a graphical representation of an exemplary eye diagram relating to the operation of a Mach-Zehnder modulator;

[0033] [Fig.7] [Fig.7] is the spectral signature of the Mach-Zehnder modulator modulated around the quadrature point;

[0034] [Fig.8] [Fig.8] is the spectral signature of the Mach-Zehnder modulator modulated around the carrier suppression point. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention relates to a photonic system provided with a photonic chip. In particular, the photonic chip according to the present invention comprises a Mach-Zehnder modulator. The photonic chip is advantageously implemented for the formation of a transmitter to which the photonic system is likely to belong.

[0036] Thus, [Fig. 2] is a schematic representation of a photonic system 10 provided with a Mach-Zehnder modulator 100 capable of being implemented within the framework of the present invention. In particular, the Mach-Zehnder modulator 100 may be formed on or in a layer, called useful layer 200 resting on a front face 310 of a support substrate 300 ([Fig. 3]).

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

[0038] The support substrate 300 may comprise any type of material, and more particularly- primarily a semiconductor material, for example Silicon.

[0039] The useful layer 200 may comprise a semiconductor material, for example silicon or a III-V material. More particularly, the useful layer 200 may rest on a layer made of dielectric material interposed between said useful layer 200 and the support substrate 300. By way of example, the Mach-Zehnder modulator may be formed on a silicon-on-insulator substrate.

[0040] The remainder of the statement also involves an optical amplifier with SOA semiconductor materials. The latter can be made of IILV semiconductor materials. In particular, the SOA can be made via either an IILV semiconductor technology on Silicon, or by hybridization of an SOA (assembly of the pre-fabricated SOA component with a silicon or SiNx waveguide) or by hybrid or heterogeneous integration (molecular bonding of IILV semiconductor materials and formation of the IILV component). In this regard, those skilled in the art may consult documents [1] and [4] cited at the end of the description.

[0041] According to the terms of the present invention, a Mach-Zehnder modulator comprises two modulation branches called, respectively, first branch 101 and second branch 102. The first branch 101 and the second branch 102 can be connected, by one of their ends, by at least one optical input 103, and, by the other of their ends, by at least one optical output 104.

[0042] More particularly, the first branch 101 and the second branch 102 each comprise a waveguide called, respectively, first waveguide 101a and second waveguide 102a. The first branch 101 and the second branch 102 each comprise a modulation section called, respectively, first modulation section 105 and second modulation section 106. The modulation section of a given modulation branch is configured to modulate the phase of a light radiation likely to be guided by the modulation branch considered.

[0043] A modulation section of a modulation branch may in particular comprise a section of the waveguide of said branch, called the modulation waveguide, and an electrode intended to impose an electrical potential on said modulation waveguide.

[0044] A modulation section is in particular configured so that an electrical potential imposed by the electrode on the modulation waveguide modifies the refractive index of the modulation waveguide in question. This index modification makes it possible to impose a phase shift on light radiation capable of being guided by the modulation section in question. In this regard, the modulation waveguide may comprise a doped silicon guide, and more particularly a silicon waveguide accommodating a PN junction. Such a waveguide has a refractive index sus capable of being modulated according to an electrical potential imposed on it. The document [2] cited at the end of the description provides an example that a person skilled in the art can implement within the framework of the present invention. The invention is however not limited to these aspects alone, and a person skilled in the art can envisage other solutions. In particular, and by way of example, the first modulation waveguide 108 and the second modulation waveguide 110 may comprise a III-V semiconductor, for example transferred by bonding to the substrate.

[0045] Thus, the modulation waveguide and the electrode of the first modulation section 105, called, respectively, first modulation guide 108 and first electrode 109, make it possible to impose a phase modulation, called first phase shift, on a light radiation guided by the first panel 101. This first phase shift is notably modulated by the electrical potential, called first potential, imposed by the first electrode 109.

[0046] Equivalently, the modulation waveguide and the electrode of the second modulation section 106, called, respectively, second modulation guide 110 and second electrode 111, make it possible to impose a phase modulation, called second phase shift, on a light radiation guided by the second panel 102. This second phase shift is notably modulated by the electrical potential, called second potential, imposed by the second electrode 111.

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

[0048] The second branch 102 generally comprises first adjustment means 107 (for example a phase shift module) configured to impose a fixed phase shift F (also called the “operating point” of the Mach-Zehnder modulator, given in radians) on a light radiation capable of being guided by said second branch 102 in addition to the phase shift -Mu(t) / 2. These two radiations guided by, respectively, the first branch 101 and the second branch 102, are then recombined at the optical output 104 to form an output radiation of intensity lout.

[0049] Thus, a light radiation, of intensity lin, injected at the optical input 103. This radiation can in particular be produced by a laser source LA, for example tunable, configured to inject said light radiation at wavelength 1 at an input of the Mach-Zehnder modulator. The light radiation is divided into two radiations intended to be guided, respectively, by the first branch 101 and the second branch 102. The radiation guided by the first branch 101, called first radiation, undergoes a phase shift equal to Mu(t) / 2, while the radiation guided by the second branch 102, called second radiation, undergoes a phase shift equal to -Mu(t) / 2 + F. These two radiations guided by, respectively, the first branch 101 and the second branch 102, are then recombined at the optical output 104 to form an output radiation of intensity lout. The intensity lout, depending on the phase shift imposed between one and the other of the modulation sections can vary between a minimum intensity Imin and a maximum intensity Imax when u(t) varies between 0 and a voltage Vpp (Vpp can for example be limited to 2V). [Fig.4] represents in this respect the transfer function (representing the intensity ratio lout / lin), represented by a sinusoidal function, of a Mach-Zehnder modulator as a function of F / pi.In order to ensure an essentially linear behavior of the Mach-Zehnder modulator, the fixed phase shift F is generally set to pi / 2 (the operating point is then said to be in "quadrature").

[0050] The 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 in the remainder of the statement.

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

[0053] ER = 10*Zogl0( )

[0054] Where Imax and Imin are the maximum and minimum intensities, respectively, achievable for a given modulation voltage Vpp (illustrated in [Fig.4]). It is generally required that this term be greater than 4 dB.

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

[0056] 0MA(dBm)= WloglO

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

[0058] Note that Imax is also defined by the intensity ILA of the radiation supplied by the laser at the input of the Mach-Zehnder modulator. More particularly, IMAX is defined by the relation IMAX = ILA x IL x cos(F), where IL represents the insertion losses, F is the phase shift (operating point) between the 2 modulation sections.

[0059] Generally, ILA is approximately equal to 10 mW (or 10 dBm)

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

[0061] Nevertheless, this condition is not without consequences on the insertion losses IL and the bandwidth BW of the Mach-Zehnder modulator. Indeed, an increase in the length L causes an increase in the insertion losses IL and reduces the bandwidth BW of the Mach-Zehnder modulator considered.

[0062] As an example, a modulation section formed in a Silicon on Insulator waveguide has the following characteristics: Losses of a modulation section of length L 22 dB x L(cm) Vpi of a modulation section of length L 1.8 V / L (cm) Bandwidth BW for a length L = 4mm for a length L = 3mm for a length L = 1.5mm 25 GHz 30GHz BW>60 GHz

[0063] Thus, a Mach-Zehnder modulator which comprises two modulation sections of a length L of the order of 0.4 cm as described in the preceding table, and operating in quadrature, has the following characteristics: Vpi 4.5 V Modulation section insertion loss 8.8 dB (IL =0.132)

[0064] Considering the following implementation conditions:

[0065] - application of a modulation voltage of u(t) / 2 = -Vpp / 2 to Vpp / 2 on each of the 'push / pull' sections (in other words, a voltage of u(t) / 2 is applied to one of the modulation sections while a voltage -u(t) / 2 to the other of the modulation sections, with Vpp= 2V);

[0066] - an intensity at the ILA input of the MZM of 10 dBm (10mW);

[0067] The intensities IMAX and IM1N are then defined by the following relations:

[0068] IMAX = ILA x IL x cos(F) x (1 + cos (Ml))

[0069] IM1N = ILA x IL x cos(F) x (l+cos(M2))

[0070] where Ml = pi / 2 + (Vpp / 2) x (pi / Vpi), and M2 = pi / 2 -(Vpp / 2) x (pi / Vpi)

[0071] Thus, these considerations make it possible to determine the extinction rate ER as well as the optical modulation amplitude OMA tabulated below: ER 6.6 dB OMA -0.7 dBm

[0072] Also, in order to increase the bandwidth BW of the Mach-Zehnder modulator, it is proposed to reduce the length L of the modulation sections. More particularly, and according to the present invention, the length L is less than a predetermined length Lp, said 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 be equal to 3 mm. Still by way of example, the predetermined length Lp may be less than or equal to 2.5 mm, and for example be equal to 2.5 mm. Still by way of example, the predetermined length Lp may be less than or equal to 2 mm, and for example be equal to 2 mm. Still as an example, the predetermined length Lp can be less than or equal to 1.5 mm, and for example be equal to 1.5 mm.

[0073] It has notably been demonstrated that a length L of the modulation sections equal to 1 mm makes it possible to obtain a bandwidth BW equal to 70 GHz. Nevertheless, such a Mach Zehnder modulator (having losses of 22 dB / cm and a value Vpi = 1.8V / L(cm)), implemented at the quadrature point, will have a Vpi of 18 V. Thus, this Mach-Zehnder modulator, modulated at a modulation voltage Vpp = 2Vpp, will have a reduced extinction ratio. As an example, and according to the conditions stated above, as soon as the length L of the modulation sections is equal to 1 mm, the extinction ratio is reduced to 1.5 dB. The OMA remains at an acceptable level of 0.2 dBm.

[0074] The extinction ratio is then much lower than the expected ratios for error-free optical transmission. In order to overcome this problem, it is possible to consider a higher modulation voltage. However, this latter consideration leads to excess consumption which is penalizing (indeed, consumption is approximately proportional to (Vpp)2). Thus, and as an example, to recover an extinction ratio of 6 dB, a modulation voltage 4 times greater is required, i.e. Vpp = 8V, and therefore consumption 16 times higher.

[0075] Herein proposed is the juxtaposition of an optical amplifier with semi-solid materials SOA conductors to the Mach-Zehnder modulator. with the following characteristics for the Mach-Zehnder modulator and the SOA, ensuring reduced overall transmitter consumption:

[0076] 1- characteristics of the Mach-Zehnder modulator: in order to maintain a voltage of low modulation (e.g. 2Vpp), while benefiting from a sufficient 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 ([Fig.5]). Considering an operating point in one of the aforementioned ranges makes it possible to increase the extinction ratio ER.

[0077] As an example, and according to these conditions, since L = 1mm, Vpp = 2V, and F = 0.85 x pi, the extinction ratio ER is equal to 6.6 dB. The optical modulation amplitude OMA associated with such an operating point is penalized, and in particular becomes equal to -3.2 dBm. This OMA value is insufficient.

[0078] 2- In order to compensate for this reduction in the OMA optical modulation amplitude, It is proposed to implement a semiconductor optical amplifier SOA at the output 104 of the Mach-Zehnder modulator. The gain of the semiconductor optical amplifier SOA is also adjusted to the loss compensation of the OMA. SOA amplifiers are generally used after propagation of the signals in the optical fiber, as repeaters, to compensate for propagation losses in the fiber (generally after several tens of kilometers) [3]. According to the present invention, the semiconductor optical amplifier SOA is integrated at the transmitter level, at the output of the Mach-Zehnder modulator. The SOA is here implemented with a gain between 3dB and 20 dB, for example equal to 3dB, or 4.8 dB, or greater than 7dB, or greater than 100 (i.e. 20 dB).

[0079] The consumption of an SOA remains low (approximately 1.2 V x 50 mA, or approximately 60 mWatt for a gain of 7 dB, or approximately 1.5 V x 120 mA for a gain of 20 dB). This additional consumption remains much lower than the overconsumption linked to the use of a modulation voltage 4 times higher (e.g. Vpp = 8 V compared to Vpp = 2 V). With a gain of 3 dB, the OMA thus becomes acceptable and equal to -0.2 dBm. Finally, the use of the SOA in low gain has another advantage: the implementation of a low gain by a low SOA control current is accompanied by a low noise factor [3].

[0080] Summary of a first implementation of the invention

[0081] The following table shows the characteristics of a Mach Zehnder modulator known from the state of the art:

[0082] ILA = lOdBm, L=4mm, BW 30 GHz Mach-Zehnder modulator operating point F Vpp ER OMA (ILA = 10 dBm) 0.5*pi 2V 6.6 dB -0.7 dBm

[0083] • According to this implementation the bandwidth is insufficient

[0084] The table given below reflects the characteristics of a Mach-Zehnder modulator operating in quadrature and for which the length of the modulation sections is reduced to 1 mm (ILA = 10dBm, L=1mm, BW 70 GHz). This reduction in length L makes it possible to appreciably increase the bandwidth. Mach-Zehnder modulator operating point F Vpp ER OMA (ILA = 10 dBm) 0.5*pi 2V 1.5 dB 0.2 dBm

[0085] The reduction in length L makes it possible to obtain an appreciable bandwidth, however the extinction rate ER remains insufficient.

[0086] The table given below reflects the characteristics of a Mach-Zehnder modulator operating in quadrature and for which the length of the modulation sections is reduced to 1 mm (ILA = 10dBm, L=1mm, BW 70 GHz). In this example, a modulation voltage 4 times higher than that proposed in the two previous tables is proposed. Operating point F of the Mach-Zehnder modulator Vpp ER OMA (ILA = 10 dBm) 0.5*pi 8 V 1.5 dB 6 dBm

[0087] Increasing the modulation voltage Vpp makes it possible to achieve an appreciable extinction rate, however the consumption of the device considered is multiplied by 16. Proposed Implementation 1:

[0088] The table given below reflects the characteristics of a Mach-Zehnder modulator operating in quadrature and for which the length of the modulation sections is reduced to 1 mm (ILA = 10 dBm, L=1 mm, BW 70 GHz). In this example, it is proposed to implement an optical amplifier with semiconductor materials (having a gain of 3 dB) and to impose a sufficiently low modulation voltage in order to limit consumption: Mach-Zehnder modulator operating point F Gain SOA Vpp ER OMA (ILA = 10 dBm) 0.85*pi 3 dB 2 V 6.6 dB -0.2 dBm

[0089] The BW, ER, OMA figures of merit are within specifications, with reduced overhead by implementing the low-gain SOA (overpower of about 40 mW).

[0090] The implementation of the present invention makes it possible both to reduce the size of a Mach-Zehnder modulator, and to give the latter a wider bandwidth compared to the modulators known from the state of the art.

[0091] Furthermore, such a Mach-Zehnder modulator provided with a reduced gain SOA allows reduced consumption and a low noise factor.

[0092] In a second embodiment, the SOA is used to reduce the intensity of the laser ILA. Indeed, it is known to those skilled in the art that a laser ages more slowly when its supply current is lower, and therefore its optical intensity ILA lower. It is also known to those skilled in the art that an SOA has a lower noise figure when it amplifies a signal of lower optical intensity at its input [3]. In this second embodiment of the invention, it is thus proposed to reduce the optical intensity ILA of the laser by 3dB, for example ILA = 7dBm, and to compensate for this reduction by increasing the gain of the SOA by 3dB, for example 6dB. The table below summarizes the advantages of this second embodiment.

[0093] By way of example, the light radiation injected by the laser source (LA) has an intensity strictly less than 10 dB, advantageously less than 7 dB. According to this scenario, the gain of the optical amplifier with semiconductor materials is adjusted so that the signal at the output of the photonic chip has an intensity equivalent to that obtained by said photonic chip without an optical amplifier with semiconductor materials and at the input of which radiation with an intensity of 10 dB would have been injected.

[0094] Second implementation mode (ILA = 7dBm, L=lmm, BW 70 GHz) Mach-Zehnder modulator operating point F Gain SOA Vpp ER OMA (ILA = 10 dBm) 0.85*pi 6 dB 2 V 6.6 dB -0.2 dBm

[0095] The BW, ER, OMA figures of merit are within specifications, with a 3dB decrease in laser intensity and reduced overconsumption by implementing SOA with a 6dB gain (overconsumption of approximately 60 mW).

[0096] [Fig.6] is a graphical representation of an example of an eye diagram relating to the operation of a Mach-Zehnder modulator. This eye diagram is in particular the result of a simulation based on a radiation intensity I LA at the input of the Mach-Zehnder modulator: 10 dBm

[0097] The modulation sections have, in the context of this simulation, a length L equal to 1.5 mm, while the gain of the optical amplifier with semiconductor materials SOA is equal to 4 (6 dB).

[0098] [Fig.6] is a graphical representation of an example of an eye diagram relating to the operation of a Mach-Zehnder modulator for which the length L of the modulation sections is 1.5mm, and an operating point f is equal to 0.75*pi.

[0099] Such a configuration makes it possible to obtain an extinction ratio ER of 5.7 dB with Vpp = 2V, and an optical modulation amplitude equal to 4.1 dBm.

[0100] The eye diagram, although slightly distorted (due to the choice of an out-of-quadrature operating point: F different from pi / 2), presents a suitable OMA and extinction ratio. In addition, the consideration of a reduced length L of the modulation sections gives the Mach-Zehnder modulator a relatively high bandwidth and in particular greater than 60 GHz.

[0101] In particular, the first adjustment means 107 comprise a first HF heating element configured to locally modify, by heating, the refractive index of one or the other of the first branch and the second branch in order to impose the fixed phase shift F.

[0102] Still advantageously, the photonic system 10 comprises first control means configured to control the first adjustment means 107.

[0103] The first control means comprise a first photodetector PDI and a first analyzer SA1. In particular, these first means are configured to electrically collect (in part) and analyze the continuous signal or the signal modulated by the Mach-Zehnder modulator 100.

[0104] A modulator M, connected to the first adjustment means 107. The modulator M can in particular be configured so that the first adjustment means 107 impose a phase shift F modulated at a modulation frequency Fd, for example equal to 5 kHz. In particular, the phase shift F can be modulated according to the following law F + F.cos (2p.Fd.t)

[0105] The implementation of such modulation makes it possible to detect the quadrature point (F=pi / 2) as well as the carrier suppression point (F=pi). In particular, when the first adjustment means 107 are modulated at the frequency Fd around the quadrature point, the radiation modulated and partially collected by the first photodetector PDI essentially comprises a harmonic at the frequency Fd. [Fig.7] represents the Fourier transform obtained by means of the first analyzer, when the latter is a spectral analyzer SA1.

[0106] Equivalently, when the first adjustment means 107 are modulated at the frequency Fd around the carrier suppression point, the modulated and partially collected radiation by the first PDI photodetector essentially comprises a harmonic at the frequency 2Fd. [Fig.8] represents the Fourier transform obtained by means of the first spectral analyzer SA1.

[0107] The adjustment of the phase shift F in the range 0.6*pi - 0.9*pi can be obtained by weighting the control signals of the first adjustment means 107 making it possible to impose the quadrature point (F=pi / 2) and the carrier suppression point.

[0108] Advantageously, the Mach-Zehnder modulator comprises a CO radiation combiner configured to combine a first radiation and a second radiation modulated in phase, respectively, by the first branch and the second branch, the first radiation and the second radiation being derived, before they are modulated by one of the modulation branches, from the division of a light radiation of a wavelength 1.

[0109] According to a particular embodiment, the CO radiation combiner comprises two output channels called, respectively, first channel VI and second channel V2.

[0110] In particular, the first channel V1 can be optically coupled with the first control guide GC1, while the second channel can carry the semiconductor material optical amplifier SOA.

[0111] The photonic chip also comprises second means for adjusting an optical gain of the semiconductor optical amplifier SOA, advantageously the second adjustment means comprise a second heating element HSOa-

[0112] The photonic system comprises second control means configured to control the second adjustment means, said second control means comprising a second photodetector PD2 and a second spectral analyzer SA2.

[0113] Advantageously, the second photodetector PD2 is carried by a second wave control guide GC2 optically coupled to the second channel V2, the coupling being dimensioned so that the second waveguide takes at most 10%, advantageously at most 5%, of the optical power circulating in the second channel V2.

[0114] The photonic chip may also comprise an optical filter FO carried by the second channel V2 and downstream of the optical amplifier with semiconductor materials SOA.

[0115] Alternatively, the first PDI photodetector may be on the SOA branch. In this case, the SOA gain is equal to the optical power on PD2 / optical power on PDI if the power draw at the output of the SOA towards PD2 is equal to the power draw at the input of the SOA towards PDI.

[0116] In a complementary manner, the photonic chip may also comprise third control means configured to determine the intensity of radiation delivered by the laser source LA. In particular, these third means of control may comprise a third photodetector PD3 configured to partially detect the laser radiation emitted by the laser source LA. This third photodetector PD3 may be coupled to an analyzer making it possible, on the sole basis of the third photodetector PD3, to determine the intensity of the light radiation emitted by the laser source LA.

[0117] These third control means are advantageously implemented to adjust the gain of the optical amplifier with semiconductor materials SOA references

[0118] [1] S. Menezo et al., “Back-Side-On-BOX heterogeneous laser integration for fully integratedphotonic circuits on Silicon" 45th European Conference on Optical Communication (ECOC 2019), 2019, pp. 1-3, doi: 10.1049 / cp.2019.0826;

[0119] [2] Reed, G et al., “Silicon optical modulators” Nature Photonics” 4, 518-526 (2010);

[0120] [3] R. Bonk, et al., "Linear semiconductor optical amplifiées for amplification of advanced modulation formats" Opt. Express 20, 9657-9672 (2012);

[0121] [4] P. Kaspar et al., "Hybrid III-V / Silicon SOA in Optical Network Based on Advanced Modulation Formats" in IEEE Photonics Technology Letters, vol. 27, no. 22, pp. 2383-2386, 15 Nov.15, 2015;

Claims

Claims

1. Photonic system provided with a photonic chip made in silicon technology, said photonic chip (10) comprising: - a Mach-Zehnder modulator (100) formed on / or in a useful layer (200) resting on one face of a support substrate (300), said Mach-Zehnder modulator comprising two modulation branches called, respectively, first branch (101) and second branch (102), each provided with a modulation section (105, 106) which extends over a length L less than 3 mm; - first means (107) for adjusting the operating point of the Mach-Zehnder modulator and configured to impose an operating point associated with a fixed phase shift F between one and the other of the first (101) and the second (102) branch;- a semiconductor optical amplifier (SOA) formed on / or in the useful layer and arranged downstream of the output (104) of the Mach-Zehnder modulator (100), said 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 so that the optical modulation amplitude associated with the photonic chip, when the fixed phase shift F is adjusted in the range 0.6*pi - 0.9*pi, is between -3 dBm and 10 dBm, at an output port S arranged downstream of the semiconductor optical amplifier SOA.;

2. A photonic system according to claim 1, wherein the first adjustment means comprise a first heating element configured to locally modify, by heating, the refractive index of either of the first branch and the second branch in order to impose the fixed phase shift F.

3. A photonic system according to claim 1 or 2, wherein said photonic system comprises first control means configured to control the first adjustment means.

4. Photonic system according to claim 3, wherein the first control means comprise a first photodetector (PDI) and a first spectral analyzer (SA1).

5. The photonic system of claim 4, wherein the Mach-Zehnder modulator (100) comprises a radiation combiner (104) configured to combine a first radiation and a second radiation phase-modulated, respectively, by the first branch (101) and the second branch (102), the first radiation and the second radiation being derived, before they are modulated by one of the modulation branches, from the division of a light radiation.

6. A photonic system according to claim 5, wherein the photonic chip (10) also comprises second means for adjusting an optical gain of the semiconductor optical amplifier (SOA), advantageously the second adjustment means comprise a second heating element (HSOa)-

7. A photonic system according to claim 6, wherein said photonic system comprises second control means configured to control the second adjustment means, said second control means comprising a second photodetector (PD2) and a second spectral analyzer (SA2).

8. Photonic system according to claim 7, in which the radiation combiner comprises two output channels called, respectively, first channel (VI) and second channel (V2), the second channel (V2) carrying the semiconductor optical amplifier (SOA), the second control means being carried by a second control waveguide (GC2) optically coupled to the second channel (V2), the coupling being dimensioned so that the second waveguide takes at most 10%, advantageously at most 5%, of the optical power circulating in the second channel (V2).

9. Photonic system according to claim 8, in which the photonic chip also comprises an optical filter (FO) carried by the first path (VI) and downstream of the semiconductor optical amplifier (SOA).

10. Photonic system according to one of claims 5 to 9 in which the photonic chip comprises a laser source (LA) configured to inject light radiation at wavelength 1 at an input of the Mach-Zehnder modulator.

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

12. Implementation of the photonic system according to one of claims 1 to 11 and in combination with claim 10 or 11, in which the light radiation injected by the laser source (LA) is of a intensity strictly less than 10 dB, advantageously less than 7 dB, and in which the gain of the optical amplifier with semiconductor materials is adjusted so that the signal at the output of the photonic chip has an intensity equivalent to that obtained by said photonic chip without an optical amplifier with semiconductor materials and at the input of which radiation with an intensity of 10 dB would have been injected.

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