Pulsed laser device comprising an active optically triggered hybrid laser source

Abstract

The invention relates to a pulsed laser device comprising: a silicon-based hybrid III / V pulsed laser source 10, having a gain section 12 and a saturable absorption section 13, both based on a photonic substrate 20, and a longitudinal waveguide 21 located in the photonic substrate 20; an optical control device 30, 40, comprising an optical pulse emitting source 31, 41 and a lateral waveguide 32, 42 located in the photonic substrate 20; the waveguides 21, 32, 42 being dimensioned such that the confinement factor Γlae / SA, Γlai / G in the quantum wells of the corresponding section 13, 12, of the optical mode of the lateral waveguide 32, 42, is greater than the confinement factor ΓL / ms, in the quantum wells of the semiconductor medium 11, of the optical mode of the waveguide Longitudinal wave 21. Figure for the abbreviation: Fig. 1A

Description

Title of the invention: Pulsed laser device comprising an active optically triggered hybrid laser source. Technical field

[0001] The field of the invention is that of neuromorphic photonics based on pulsed neural networks. More specifically, the invention relates to a pulsed laser device capable of forming a photonic neuron, and comprising a pulsed laser source. PREVIOUS STATE OF THE ART

[0002] Neuromorphic computing is currently undergoing rapid development, particularly to meet the demands of intensive data processing. Artificial neural networks (ANNs) have demonstrated their power and efficiency in this regard. Such artificial neurons can be fabricated using pulsed laser sources on photonic chips, hence the terms neuromorphic photonics and spiked photonic neurons.

[0003] A general presentation of impulse photonic neurons can be found, in particular, in the article by Shastri et al. entitled Principles of Neuromorphic Photonics, arXiv: 1801.00016, 2018. An impulse photonic neuron may comprise: a set of input ports, each providing an input signal Xi with i ranging from 1 to m, each input signal x being weighted by a weight w of positive or negative sign; and a combiner performing the summation of the weighted input signals WjXj, associated with an activation function. The artificial neuron provides an output signal y when the sum of the weighted input signals exceeds a predefined threshold. In the case of impulse photonic neurons, the output signal is an optical spike.Following the emission of an optical pulse by the impulse photonic neuron, it enters a so-called refractory period, in which it does not emit any output optical pulses, regardless of the input signals.

[0004] Such impulse photonic neurons can be classified into two categories: a first category called 'all optical' in which the input signals remain in the optical domain until the laser source; and a second category called 'optical / electrical / optical' (O / E / O) in which the input signals pass from the optical domain to the electrical domain, to return to the optical domain.

[0005] The article by Robertson et al. entitled Ultrafast optical integration and pattern classification for neuromorphic photonics based on spiking VCSEL neurons, Sci Rep. 2020 Apr 8;10:6098 describes an all-optical, pulsed photon neuron. It consists of a vertical cavity surface-emitting laser (VCSEL) coupled to an excitation laser. The excitation optical pulse must have a wavelength shifted relative to the wavelength of the optical cavity of the VCSEL. Furthermore, the excitation optical pulses must be inverted, meaning that the abrupt decrease in incident optical power is what excites the neuron formed by the VCSEL. This pulsed photon neuron therefore has the disadvantage of requiring several optoelectronic devices for inverting the optical pulses and for strictly controlling the wavelength shift.

[0006] Furthermore, the article by Peng et al. entitled "Neuromorphic Photonic Integrated Circuits," IEEE J. Sel. Topics Quantum Electron., vol. 24, no. 6, 2018, describes a pulsed O / E / O type photonic neuron. This neuron comprises a pulsed laser source with distributed feedback (DFB) whose semiconductor medium has two electrically isolated sections: a gain section (gain medium) and a saturable absorber section. The laser source is triggered by optical pulses converted into electrical pulses by a pair of photodiodes and then injected into the gain section. These electrical pulses form excitatory or inhibitory synaptic signals. However, O / E conversions can generate additional losses that can reduce the bandwidth of the pulsed photon neuron as well as the intensity or power of the emitted laser pulse.Furthermore, the photodiode pairs complicate the triggering circuit and reduce the surface density of the photonic neural network.

[0007] We also know of the scientific article by Uenohara et al. entitled Operation Characteristics of a Side-Light-Injection Multiple-Quantum-Well Bistable Laser for All-Optical Switching, Jpn. J. appl. Phys. Vol. 33 (1994), pp.815-821. However, it deals with a bistable laser and not with a pulsed laser. Description of the invention

[0008] The invention aims to remedy at least in part the drawbacks of the prior art, and to propose a pulsed laser device comprising a hybrid pulsed laser source in IILV technology on silicon, forming an optically active triggered (i.e. all-optical) photonic artificial neuron and exhibiting optimized performance.

[0009] For this purpose, the object of the invention is a pulsed laser device comprising a pulsed laser source and at least one optical control device.

[0010] The pulsed laser source is a silicon-based III-V hybrid laser source. It comprises a semiconductor medium with quantum wells, made from a III-V compound, located in an optical cavity defining a longitudinal axis, and comprising at least one gain section and at least one saturable absorbing section where the quantum wells are coplanar.

[0011] The laser source also includes a photonic substrate, made of silicon, on which the semiconductor medium rests, and in which is located a longitudinal waveguide participating in defining the optical cavity and optically coupled to the semiconductor medium along the longitudinal axis, the longitudinal waveguide having a width lL / ms and a vertical spacing dL / ms with respect to the semiconductor medium, in a coupling zone zcL / ms with the semiconductor medium, predefined so that the optical mode propagating in the longitudinal waveguide has a confinement factor E / ^.in the quantum wells of the semiconductor medium.

[0012] Furthermore, the optical control device comprises: at least one emitting source adapted to emit at least one optical control pulse of predefined intensity; and at least one lateral waveguide.

[0013] The lateral waveguide is located in the photonic substrate and is optically coupled to the saturable absorbing section or the gain section for transmitting the optical control pulse, inclined with respect to the longitudinal axis to avoid optical coupling with the optical cavity. It has a predefined width and vertical spacing with respect to the semiconductor medium, in a coupling region with said corresponding section, such that the optical mode propagating in the lateral waveguide has a confinement factor in the quantum wells of said corresponding section greater than Et / ms-

[0014] Furthermore, the longitudinal waveguide may have a width of lL / ms in its coupling zone zcL / ms, and the lateral waveguide has a width in its coupling zone less than lL / ms.

[0015] The longitudinal waveguide may have a vertical spacing dl / m, in its coupling zone zcL / ms with respect to the quantum wells of the semiconductor medium, and the lateral waveguide may have a vertical spacing in its coupling zone with respect to the quantum wells of the semiconductor medium, where the vertical spacing dL / ms is greater than or equal to that of the lateral waveguide.

[0016] The longitudinal waveguide and the lateral waveguide can be edge waveguides formed of a base and an edge, the lower face of the longitudinal waveguide and that of the lateral waveguide being coplanar.

[0017] The longitudinal waveguide can extend continuously under the semiconductor medium.

[0018] The lateral waveguide may extend continuously under the corresponding section or includes at least one coupler at the tip.

[0019] The semiconductor medium may include at least two gain sections located on either side of the saturable absorbing section.

[0020] The gain section and the saturable absorption section can be physically distant portions of each other, or can be areas of the same plot formed by the semiconductor medium.

[0021] The optical control device can be an optical excitation device, the emitting source being adapted to emit at least one optical excitation pulse of predefined intensity. The lateral waveguide, referred to as the excitation waveguide, can then be optically coupled to the saturable absorbing section. The optical mode propagating in the lateral excitation waveguide then exhibits a confinement factor riae / SA in the quantum wells of the saturable absorbing section greater than Lums-

[0022] The optical control device can be an optical inhibition device, the emitting source being adapted to emit at least one optical inhibition pulse of predefined intensity. The lateral waveguide, referred to as the inhibition waveguide, can then be optically coupled to the gain section. The optical mode propagating in the lateral inhibition waveguide then exhibits a confinement factor Liai / G in the quantum wells of the gain section greater than rL / ms.

[0023] The pulsed laser device may include an optical excitation device and an optical inhibition device.

[0024] The pulsed laser device may include optical intensity attenuators arranged on the lateral waveguides, and adapted to reduce the intensity of the optical excitation and inhibition pulses.

[0025] The invention also relates to a photonic artificial neural network, comprising a plurality of pulsed laser devices according to any one of the preceding characteristics, in which each pulsed laser source forms a photonic artificial neuron, the photonic artificial neurons being optically connected to each other.

[0026] In this photonic artificial neural network, a longitudinal waveguide of a pulsed laser device can form a lateral excitation or inhibition waveguide of another pulsed laser device.

[0027] The invention also relates to a method of using a pulsed laser device according to any one of the preceding characteristics, comprising the following steps: - forward biasing of the gain section by an electric current of a predefined constant intensity so that the gain g of the semiconductor medium reaches a maximum value gmax, and application of a zero or reverse bias of the saturable absorbing section; - emission of an optical excitation pulse by the optical excitation device, causing emission of a laser pulse by the pulsed laser source if the gain is at least equal to an excitability value gexc - emission of an optical inhibition pulse by the optical inhibition device, preventing the emission of a laser pulse by a decrease in the value of the gain below the excitability value gexc. Brief description of the drawings

[0028] Other aspects, objects, advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0029] Figures IA and IB are schematic and partial views, in perspective ([Fig.1A]) and in longitudinal section ([Fig.1B]), of a pulsed laser device according to one embodiment;

[0030] [Fig.2] is a schematic and partial view of a pulsed laser device according to one embodiment, forming a network of photonic artificial neurons;

[0031] [Fig.3] is an example of the evolution, as a function of the width 1 of the integrated waveguide, of the confinement factor F of an optical mode, circulating in the integrated waveguide, in the quantum wells of a semiconductor medium optically coupled to the integrated waveguide;

[0032] [Fig.4A] is a schematic and partial cross-sectional view of the gain section and the longitudinal waveguide according to one embodiment, and Figures 4B and 4C are top views of the longitudinal waveguide according to exemplary embodiments;

[0033] [Fig.5A] is a schematic and partial cross-sectional view of the saturable absorbing section and the lateral excitation waveguide according to one embodiment, and Figures 5B to 5D are top views of the lateral waveguide according to exemplary embodiments;

[0034] Figures 6A and 6B are schematic and partial views, in perspective ([Fig.ôA]) and from above ([Fig.ôB]), of a pulsed laser device according to another embodiment, and [Fig.ôC] is a perspective view of a longitudinal waveguide and the lateral excitation waveguide illustrated in [Fig.ôA] and 6B.

[0035] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0036] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

[0037] [Fig.1A] is a schematic and partial perspective view of a pulsed laser device 1 according to one embodiment, and [Fig.1B] is a longitudinal cross-sectional view of the semiconductor medium 11 and the longitudinal waveguide 21 illustrated in [Fig.1A].

[0038] Here and for the remainder of the description, a three-dimensional orthogonal XYZ direct frame is defined, where the XY plane is a plane parallel to the plane of the photonic substrate 20, and where the Z axis is oriented from the photonic substrate 20 towards the semiconductor medium 11 of the laser source 10. Furthermore, the terms "lower" and "upper" are understood as relating to an increasing positioning when moving away from the photonic substrate 20 along the +Z direction.

[0039] The pulsed laser device 1 comprises at a minimum: a pulsed, hybrid III / V silicon laser source 10; and at least one optical control device 30, 40, adapted to cause or inhibit the emission of a laser pulse by the laser source 10.

[0040] The laser source 10 is said to be pulsed insofar as it is adapted to emit laser pulses. It is optically active triggered since the emission of the laser pulse is triggered or prevented by means of optical excitation and inhibition pulses that are transmitted directly to the laser source 10, without passing through photodiodes ensuring O / E conversion. The triggering of the laser emission is therefore not achieved by modulating the pump's electrical current. This laser source 10 thus belongs to the 'all-optical' category of pulsed laser sources with triggered mode.

[0041] This pulsed laser device 1 is here part of a photonic artificial neural network (see [Fig. 2]). More precisely, the laser source 10 forms a photonic artificial neuron. The lateral waveguides 32, 42 are the synapses and ensure the transmission of synaptic excitation and inhibition signals to the laser source 10. As detailed below, the laser source 10 exhibits properties characteristic of physiological neurons, such as excitability and refractory period (described later).

[0042] The laser source 10 is described as a silicon-based hybrid 111 / V laser source, in that it comprises a semiconductor medium 11 made from a III-V compound resting on a silicon-based photonic substrate 20. The optical cavity is delimited here by two optical reflectors 22, in this case Bragg mirrors (distributed Bragg reflector, DBR, laser source), located in an integrated longitudinal waveguide 21 arranged in the photonic substrate 20. However, the optical cavity can also be of the distributed feedback (DFB) type, where a single Bragg grating extends along the longitudinal waveguide 21 over the entire length of the optical cavity, or even be of the ring type, or of the Sagnac loop mirror type. The optical cavity defines a longitudinal axis X along which the longitudinal waveguide 21 extends.

[0043] The photonic substrate 20 is formed of a support substrate and waveguides 21, 32, 42 integrated within the support substrate. It may include other passive optical components (multiplexers or demultiplexers, optical fiber couplers, etc.) and / or active optical components (modulators, etc.), optically coupled to each other to form an integrated photonic circuit. The photonic substrate 20 may be of the SOI type, that is, it may comprise a thin layer of silicon and a silicon support substrate, between which is intercalated a layer of oxide called BOX (buried oxide). The waveguides 21, 32, 42 may have a core made of silicon and a cladding made of silicon oxide. In this example, the integrated waveguides 21, 32, 42 are, preferably at least in a coupling zone with the semiconductor medium 11, edge guides formed of an edge (rib) resting on a base (slab).The longitudinal waveguide 21 is separated from the semiconductor medium 11 by a silicon oxide layer 23 of a preferably constant local thickness egap. In [Fig. 4A], the base is labeled 21.1 and the edge is labeled 21.2.

[0044] The semiconductor medium 11 rests on the photonic substrate 20 and is located in the optical cavity. It is optically coupled to the longitudinal waveguide 21 above which it is situated. It is made of a semiconductor compound, here of type III-V. The term III-V refers to columns III and V of the periodic table of elements. In this example, it comprises a semiconductor layer 11.2 containing multiple quantum wells, for example made of InGaAsP or AlGalnAs with a maximum gain, for example, centered on the wavelength of the laser pulse. The quantum well layer 11.2 is flanked along the vertical Z-axis by doped semiconductor layers, for example made of InP, here by a lower n-doped layer 11.1 and an upper p-doped layer 11.3. Also, the semiconductor medium 11 comprises a PIN junction that extends longitudinally in the XY plane. The semiconductor medium 11 forms an active waveguide optically coupled to the longitudinal waveguide 21.

[0045] The semiconductor medium 11 is formed of at least one gain section 12 (optical amplification) and at least one saturable absorption section 13. In this example, the semiconductor medium 11 comprises one gain section 12 and one saturable absorption section 13, but it may also comprise two gain sections located on either side of a saturable absorption section 13 (see [Fig. 6A]), or even more. It may comprise more gain sections and saturable absorption sections. These sections 12, 13 are arranged relative to each other on the longitudinal axis X of the optical cavity. Furthermore, they are electrically isolated from each other so that electrical pumping of one section does not alter the free carrier density of the other section. Finally, these sections can be physically separated blocks (see [Fig.1A] and IB), or can be electrically isolated areas of the same block (see [Fig.6A] and 6B).

[0046] The gain section 12 is the principal site of optical amplification of the optical mode present in the optical cavity. It is formed from the gain medium of the laser source 10, here constituted by the InP-based semiconductor compound. It is electrically connected to a polarizing power source (not shown), which provides forward biasing of the gain section 12. The pump current intensity is defined such that the gain g of the semiconductor medium 11 reaches, in steady state, a constant maximum value gmax. The gain g is, in a known manner, correlated with the density nG of free carriers injected into the gain section 12 by the power source (electrical pumping).Furthermore, the steady-state regime, as detailed later, corresponds to the regime where the gain is maximum and constant and where no optical pulse is received by the gain section 12 and by the saturable absorbing section 13 (the optical losses in the optical cavity are then sufficiently high to prevent the emission of a laser pulse). Here, the optical losses are essentially associated with the transmission coefficient of the material of the saturable absorbing section 13.

[0047] The saturable absorbing section 13 has a controllable optical shutter function. As is known, a saturable absorber is a medium whose optical transmission coefficient, at the wavelength of the laser emission, varies with the incident optical intensity. Thus, the transmission is low or even negligible at low incident optical intensities, while it is high at high optical intensities (the material then becomes transparent). The saturable absorbing section 13 can then occupy two principal states and one intermediate state: - a resting state, called the blocking state, when the incident optical intensity is low. In this state, the transmission coefficient is low so that the optical losses in the optical cavity are high, at least equal to a predefined amax value; - a forward-biased state, when the incident optical intensity is high. In this state, the transmission coefficient is high (the material is transparent to the wavelength of the laser emission) so that optical losses are low, at most equal to a predefined value. The material is said to be saturated. - an intermediate state, for which the optical losses are between amin and amax (values ​​not included). The material is then subjected to an incident light beam, but is not saturated.

[0048] In this example, the saturable absorber section 13 has a semiconductor heterostructure identical to that of the gain section 12 in terms of material, doping, and layer thickness. Also, the quantum wells of the gain section 12 and those of the saturable absorber section 13 are coplanar. Furthermore, unlike the gain section 12, the saturable absorber section 13 is not forward-biased, but is either reverse-biased or has a zero potential difference. Finally, it advantageously has a length along the longitudinal axis X that is shorter than that of the gain section 12 (and, where applicable, shorter than the cumulative length of the gain sections), and preferably has a length between approximately 2% and 10% of this cumulative length. Thus, the saturable absorber section 13 exhibits a saturation / desaturation dynamics conducive to the emission of particularly short and intense laser pulses.

[0049] By way of example, the semiconductor heterostructure of the gain section 12 and the saturable absorption section 13 is formed of a lower semiconductor layer 11.1 of n-doped InP with a thickness of 150 nm. It comprises a quantum-well semiconductor layer 11.2 based on AlGalnAs with a thickness of 300 nm, and an upper semiconductor layer 11.3 of InP with a thickness of approximately 2 pm. The length of the gain section 12 can be equal to 600 pm and that of the saturable absorption section 13 can be equal to 20 pm.

[0050] The electrical biasing source (not shown) thus provides forward biasing to the gain section 12 (electrical pumping) and applies zero bias to the saturable absorbing section 13 (ISA=0mA). Alternatively, it can apply reverse bias. The electrical source transmits a predefined direct current to the gain section 12, such that the gain tends towards a maximum steady-state value gmax. This maximum value gmax is less than the optical losses amax when the saturable absorbing section 13 is in the blocking state (here, when it is not illuminated by an optical pulse). originating from the optical excitation device 30 and of sufficient power to make section 13 transparent), so as to avoid the emission of a continuous laser signal.

[0051] Thus, by way of example, the threshold current can be equal to 16 mA, a value for which the gain gth (greater than the value gmax) balances the high optical losses amax of the saturable absorbing section 13 in the blocking state, thereby causing the emission of a succession of laser pulses. Therefore, in order to be able to actively "trigger" the emission of a laser pulse, the value of the pump current is set to a value lower than this threshold current, for example to approximately 15 mA, so that the maximum value gmax of the steady-state gain is well below the threshold value g* and therefore does not balance the maximum optical losses amax.On the other hand, as detailed later, the value gmax of the gain is high enough to be at least equal to the optical losses amin when the saturable absorbing section 13 occupies the on-state (here when it is illuminated by an optical pulse from the optical excitation device 30).

[0052] The pulsed laser device 1 comprises one or more optical control devices 30, 40, and in this example comprises an optical excitation device 30 and an optical inhibition device 40. It can obviously comprise several optical excitation devices 30 and / or several optical inhibition devices 40.

[0053] Each optical control device 30, 40 comprises: at least one emitting source 31, 41 adapted to emit at least one optical control pulse of predefined intensity; and at least one lateral waveguide 32, 42. The same emitting source can be coupled to one or more lateral waveguides, and the same lateral waveguide can be coupled to one or more emitting sources.

[0054] The emitting source 31, 41 can be located on the photonic substrate 20 (as illustrated in [Fig. 1A]), but alternatively, it can be located outside the photonic substrate 20 while being coupled to the lateral waveguide by an optical coupler. Active or passive optical elements (modulator, multiplexer, coupling network, etc.) can be coupled to the lateral waveguide and located between the corresponding emitting source and the semiconductor medium 11.

[0055] As detailed later, each lateral waveguide has dimensional properties in terms of width and vertical spacing, in a coupling zone with the corresponding section of the semiconductor medium 11 (i.e. the saturable absorbing section 13 in the case of excitation, and the gain section 12 in the case of inhibition), predefined such that the confinement factor of the optical mode in the quantum wells of the corresponding section is greater than the confinement factor of the optical mode (propagating in the longitudinal waveguide 21) in the quantum wells of the semiconductor medium 11.

[0056] The optical excitation device 30 comprises an emitting source 31 adapted to emit an optical excitation pulse, and a lateral waveguide 32 for transmitting the optical excitation pulse to the saturable absorbing section 13. This lateral waveguide 32 is integrated into the photonic substrate 20 and is optically coupled to the saturable absorbing section 13 without being optically coupled to the optical cavity. To achieve this, the lateral waveguide 32 is coupled to the saturable absorbing section 13 at an angle in the XY plane with respect to the longitudinal axis X. Therefore, the photons of the optical excitation pulse, not absorbed by the saturable absorbing section 13, do not propagate along the longitudinal axis X in the optical cavity.In this example, the tilt angle formed by the lateral waveguide 32 with respect to the longitudinal axis X, at the level of the saturable absorbing section 13, is for example between 60° and 120°. In this example, it is approximately 90°. Preferably, it is coplanar with the longitudinal waveguide 21 (it can be made from the same single-crystal silicon thin layer of an SOI substrate), in the sense that the lower face of the lateral waveguide 32 is coplanar with that of the longitudinal waveguide 21.

[0057] The optical excitation pulse has a predefined optical intensity and a wavelength here equal to the wavelength of the laser oscillation (included in the absorption spectrum of the saturable absorbing section 13). It can cause the laser source 10 to emit a laser pulse when the gain reaches its maximum steady-state value gmax. As detailed below, the fact that the gain reaches this maximum value gmax indicates that the laser source 10 is indeed capable of emitting a laser pulse: this is then followed by a so-called refractory period during which it is unable to emit a laser pulse, even if it has received an optical excitation pulse.

[0058] In other words, when the saturable absorbing section 13 is not illuminated by the optical excitation pulse, it exhibits minimal transmission, resulting in maximum optical losses amax. The pump current injects a density of free carriers into the gain section 12, resulting, in steady state, in a maximum gain value gmax. This maximum value gmax is less than a threshold value gth that would balance the maximum optical losses amax of the saturable absorbing section 13 and cause the emission of a laser signal. Therefore, in steady state, the laser source 10 does not receive an optical excitation pulse and thus does not emit a laser pulse.

[0059] On the other hand, when the saturable absorbing section 13 is saturated, it exhibits maximum transmission, resulting in minimal optical losses. The maximum value gmax of the gain is then at least equal to the minimum value amin of the optical losses, so that, when the saturable absorber section is illuminated by the excitation optical pulse and is saturated, the laser source 10 then emits an optical pulse.

[0060] The pulsed laser device 1 may also include an optical inhibition device 40. This device comprises an emitting source 41 adapted to emit an optical pulse called an inhibition pulse, and a lateral inhibition waveguide 42 for transmitting the optical inhibition pulse to the gain section 12. This lateral waveguide 42 is also integrated into the photonic substrate 20 and is optically coupled to the gain section 12 without being optically coupled to the optical cavity. For this purpose, as with the lateral waveguide 32, the lateral waveguide 42 is coupled to the gain section 12 at an angle in the XY plane with respect to the longitudinal axis X. Therefore, the photons of the optical inhibition pulse do not propagate along the longitudinal axis X in the optical cavity. In this example, the angle of inclination is between 60° and 120°, and here is approximately 90°.Preferably, it is coplanar with the longitudinal waveguide 21 (it can be made from the same single-crystal silicon thin layer of an SOI substrate), in the sense that the lower face of the lateral waveguide 42 is coplanar with that of the longitudinal waveguide 21.

[0061] The inhibiting optical pulse has a predefined optical intensity and here a wavelength equal to that of the laser oscillation. It can prevent the emission of a laser pulse by the laser source 10. For this purpose, as detailed later, such an optical pulse received by the gain section 12 causes a decrease in the value of the gain, which then has a transient value lower than the maximum value gmax, but also lower than a so-called excitability value gexc from which the laser source 10 can emit a laser pulse when the saturable absorbing section 13 receives the excitation optical pulse and is saturated.

[0062] In other words, when the gain has a value, in steady state, greater than or equal to the excitability value gexc but less than the threshold value gth (and therefore less than the maximum optical losses amax), the laser source 10 emits a laser pulse or not, depending on whether the saturable absorbing section 13 receives an optical excitation pulse or not. Conversely, when the gain has a transient value less than the excitability value gexc, the laser source 10 does not emit a laser pulse, even if the saturable absorbing section 13 receives an optical excitation pulse.

[0063] Figure 2 is a schematic and partial view of a pulsed laser device 1 according to an embodiment in which it corresponds to an artificial neural network. photonics. The laser source 10 forms a photonic artificial neuron, which is connected to the optical excitation devices 30 and inhibition devices 40 by their lateral waveguides. These lateral waveguides thus form the synapses of the photonic artificial neuron 10. In this example, the optical excitation devices 30 and inhibition devices 40 are pulsed laser sources identical or similar to that of the pulsed laser device 1, and therefore also form photonic artificial neurons.

[0064] The assembly here is part of an active-triggered, all-optical photonic artificial neural network in a hybrid III / V configuration on silicon, where the various waveguides are integrated into the photonic substrate. The excitation optical pulses are therefore synaptic signals with a positive weight, the intensity of which can be modified by optical intensity attenuators. Similarly, the inhibition optical pulses are synaptic signals with a negative weight, the intensity of which can also be modified.

[0065] Note that the pulsed laser device 1 may include intensity attenuators 2 (see [Fig. 2]), coupled to the lateral waveguides 32, 42, to attenuate or not the intensity of the transmitted optical excitation and inhibition pulses. Such attenuators 2 may be Mach-Zehnder or resonant ring modulators. They may also be phase-change materials chosen particularly from among the chalcogenides, especially of the GST type, i.e., formed from germanium Ge, antimony Sb, and tellurium Te. Reference may be made to the document by Abdollahramezani et al. entitled "Tunable nanophotonics enabled by chalcogenide phase-change materials," Nanophotonics 2020, 9(5), 1189-1241.

[0066] In the following description, TL / ms denotes the confinement factor in the quantum wells of the semiconductor medium 11 of the optical mode propagating in the longitudinal waveguide 21. Similarly, Tiae / sA denotes the confinement factor in the quantum wells of the saturable absorbing section 13 of the optical mode propagating in the lateral excitation waveguide 32. And finally, Liai / G denotes the confinement factor in the quantum wells of the gain section 12 of the optical mode propagating in the lateral inhibition waveguide 42.

[0067] The longitudinal waveguide 21, the lateral waveguide 32, and the lateral waveguide 42 have predefined dimensional properties in their respective coupling zones, so that the confinement factor Tiae / sA and the confinement factor rlai / G are greater than the confinement factor TL / ms.

[0068] More precisely, the dimensional properties are mainly the width 1 of the integrated waveguides and their vertical spacing d with respect to the semiconductor medium 11 (and therefore with respect to the quantum wells of the latter). The waveguide The longitudinal waveguide 21 therefore has a width lL / ms and a vertical spacing dl / m^ which are defined in a coupling zone zL / ms with the semiconductor medium 11, so that the optical mode circulating in the longitudinal waveguide 21 has a confinement factor rL / ms in the quantum wells of the semiconductor medium 11.

[0069] The waveguides 21, 32, 42 can be edge waveguides formed of a base and an edge. The edge can be located on the side of the semiconductor medium 11, as illustrated in [Fig. 4A], 5A and 6A, but alternatively it can be located on the opposite side. The width 1 of the waveguide is then the distance, along a transverse axis in the XY plane, between the lateral flanks of the edge. In the case of a waveguide with a rectangular cross-section (no edge), the width 1 is then the transverse distance in the XY plane between the flanks of the waveguide. Furthermore, the vertical spacing d is the distance, along the Z axis, between the upper face of the waveguide (in the case of an edge-guide: upper face of the edge or of the base, depending on the position of the edge) and the lower face of the semiconductor medium 11.

[0070] Similarly, the lateral waveguide 32 therefore has a width liae / sA and a vertical spacing diae / SA, which are defined in a coupling zone Ziae / SA with the saturable absorbing section 13, such that the optical mode circulating in the lateral waveguide 32 has a confinement factor riae / SA in the quantum wells of the saturable absorbing section 13. The width liae / sA and the vertical spacing diae / sA are predefined so that riae / SA is greater than rL / ms, for example 10 times greater.

[0071] Finally, the lateral waveguide 42 has a width liai / G and a vertical spacing diai / G, which are defined in a coupling zone Ziai / G with the gain section 12, such that the optical mode circulating in the lateral waveguide 42 has a confinement factor ^ / 0 in the quantum wells of the gain section 12. The width liai / G and the vertical spacing diai / G are predefined so that Eià / c is greater than rL / ms, for example 10 times greater.

[0072] This then makes it possible to improve the performance of the pulsed laser device 1. Indeed, when the optical mode circulating in the optical cavity, and therefore in the longitudinal waveguide 21, has a confinement factor rL / ms in the quantum wells of the semiconductor medium 11, which is low, for example on the order of 1 to 2%, the saturated gain of the laser source 10 is high, which makes it possible to obtain higher energy laser pulses. It is therefore desirable to keep the value of the confinement factor rL / ms low.

[0073] On the other hand, when the optical modes of the control signals, i.e. those circulating in the lateral waveguides 32 and 42, exhibit a high confinement factor in the quantum wells of the saturable absorbing section 13 (for the optical mode circulating in the guide 32) and in those of the gain section 12 (For the optical mode circulating in the waveguide 42), both emission and inhibition efficiency are optimized. Indeed, photons injected laterally into the saturable absorbing section 13 induce a maximum of free carrier excitation, which locally increases population inversion and thus saturates absorption more effectively. Similarly, photons injected laterally into the gain section 12 induce a maximum of stimulated emission, which locally decreases population inversion and thus effectively reduces the gain.

[0074] In this configuration, the optical mode propagating in the longitudinal waveguide 21 exhibits a low confinement factor rL / ms in the quantum wells of the semiconductor medium 11, while the optical mode propagating in the lateral waveguide 32 exhibits a higher confinement factor Eiae / sA in the quantum wells of the saturable absorbing section 13 (just like the lateral waveguide 42 which exhibits a higher confinement factor Fiai / G).

[0075] Also, within the framework of a pulsed laser device 1 according to the invention, where the laser source 10 has a III-V configuration on Si, it is possible to optimize the performance simply by adjusting the width lL / ms and / or the vertical spacing dL / ms of the longitudinal waveguide 21 in its coupling region zcL / ms with the semiconductor medium 11, and by adjusting the width liae / sA and / or the vertical spacing diae / SA of the lateral waveguide 32 in the coupling region zciae / sA. Similarly, the width liai / G and / or the vertical spacing diai / G of the lateral waveguide 42 in its coupling region zciai / G with the gain section 12 can be adjusted. This takes advantage of the fact that the waveguides 21, 32, and 42 are waveguides integrated into the photonic substrate. 20, and whose width and vertical spacing parameters can be adjusted simply, independently of the semiconductor medium 11.

[0076] Fig. 3 illustrates an example of the evolution of the confinement factor T of an optical mode, propagating in an edge-integrated waveguide, in the quantum wells of the semiconductor medium 11, as a function of the width 1 of the waveguide, and here of its edge.

[0077] In this example, the semiconductor medium 11 comprises a lower portion 11.1 of n-type doped InP with a thickness of 150 nm. Portion 11.2 is formed of a lower confinement portion of AlGalnAs with a thickness of 90 nm, a central quantum well portion based on AlGalnAs with a thickness of 120 nm, and an upper confinement portion of InGaAsP with a thickness of 90 nm. The upper portion 11.3 of p-type doped InP has a thickness of 2 pm. Portions 11.2 and 11.3 have a width of 5 pm.

[0078] Furthermore, by way of example, the integrated waveguide is made of silicon and is surrounded by a silicon oxide. It consists of a base 21.1 with a width of 15pm and a thickness of 300nm, and an edge 21.2 with a width 1 to be varied and a thickness of 200nm. The waveguide is vertically spaced from the semiconductor medium 11 by a distance of lOOnm.

[0079] The confinement factor F of the optical mode in quantum wells is determined by the Lumerical software for numerical simulation of the equations of electromagnetism using the MODE-FDE mode solver. It appears that the confinement factor F is a decreasing function with the width 1 of the waveguide, and exhibits a sharp decrease around a threshold value, here on the order of 0.6 pm. It also appears that it is possible, both simply and simultaneously, to adjust the width lL / ms of the longitudinal waveguide 21 in its coupling zone with the semiconductor medium 11 so that the confinement factor rL / ms is around 1 to 2%, and to adjust the width liæ / sA of the lateral waveguide 32 in its coupling zone with the saturable absorbing section 13, and the width liai / G of the lateral waveguide 42 in its coupling zone with the gain section 12, so that the respective confinement factors Fiae / SA and Fiai / G are maximal, and here around 13%.

[0080] Preferably, the vertical spacing d of the integrated waveguides 21, 32, 42 with respect to the semiconductor medium 11, and therefore with respect to the quantum wells, are identical. The lateral waveguides 32, 42 then have respective widths liae / sA and liai / G that are less than the width lL / ms of the longitudinal waveguide 21. This is illustrated in Figures 4A-4C and 5A-5D. Alternatively, or in addition, the respective vertical spacing diae / SA and diai / G of the lateral waveguides 32, 42 can be less than the vertical spacing dL / ms of the longitudinal waveguide 21.

[0081] Figure 4A is a schematic and partial cross-sectional view of the gain section 12 and the longitudinal waveguide 21. The width lL / ms of the longitudinal waveguide 21 is that of its edge 21.2 in the coupling region zcL / ms, since this parameter affects the confinement factor rL / ms. The edge 21.2 has a top face opposite the base 21.1, and lateral flanks. These are substantially vertical. As previously stated, the width lL / ms is the transverse distance, along the Y-axis, between the lateral flanks of the edge 21.2. The vertical spacing dL / ms is the distance along the Z axis, defined in the coupling zone zct / ms, between the upper face of the edge 21.2 and the lower face of the semiconductor medium 11. In this example, dL / ms is equal to diae / SA and to diai / G.

[0082] Figure 4B is a schematic and partial top view of the longitudinal waveguide 21 according to an exemplary embodiment. The coupling zone with the semiconductor medium 11 is shown as a dashed line. The gain section 12 and the saturable absorbing section 13 are therefore located in this coupling zone. In this example, the longitudinal waveguide 21 has an edge 21.2 with a width The minimum constant lL>min is present in the upstream and downstream zones of the coupling zone zcL / ms, this width being less than the value 1. For example, the width 1L can be equal to 400 nm while the width lL / ms can be equal to 700 nm. The longitudinal waveguide 21 exhibits intermediate zones where the width changes from the value lL>min to the value 1.

[0083] Figure 4C is a schematic and partial top view of the longitudinal waveguide 21 according to another embodiment. In this example, the longitudinal waveguide 21 has a rectangular cross-section upstream and downstream of the coupling zone. Indeed, the width 1L of the edge increases from the coupling zone zcums until it reaches the width of the base 21.1, for example here 15 pm. The longitudinal waveguide 21 therefore has intermediate zones where the width goes from the maximum value 1L>max to the value 1 / 2 µm-

[0084] Figure 5A is a schematic and partial cross-sectional view of the saturable absorbing section 13 and the lateral waveguide 32. The width liae / sA of the lateral waveguide 32 is here that of its edge 32.2 in the coupling zone zciae / sA. The edge 32.2 has a top face opposite the base 32.1, and lateral flanks. These are also substantially vertical here. The width liae / sA is the transverse distance, along the X-axis, between the lateral flanks of the edge 32.2. The vertical spacing diae / SA is the distance along the Z axis, defined in the coupling zone zciae / sA, between the upper face of the edge 32.2 and the lower face of the saturable absorbing section 13 of the semiconductor medium 11. In this example, dL / ms is equal to diae / SA and to d^ / G.

[0085] Figure 5B is a schematic and partial top view of the lateral waveguide 32 according to an exemplary embodiment. The coupling zone zciae / sA with the saturable absorbing section 13 is shown as a dashed line (the saturable absorbing section 13 is therefore located in this coupling zone). In this example, the lateral waveguide 32 has an edge of constant width liae / sA both in the coupling zone zciae / SA and in the upstream and downstream zones. By way of example, the width liae / sA can be equal to 400 nm.

[0086] Figure 5C is a schematic and partial top view of the lateral waveguide 32 according to another embodiment. In this example, it is a waveguide with a rectangular cross-section upstream and downstream of the coupling zone zciae / SA. Indeed, the edge width increases from the coupling zone until it reaches the width of the base 32.1, for example, 15 pm here. The lateral waveguide 32 has intermediate zones where the width decreases from the maximum value liae>max to the value liae / sA-

[0087] Figure 5D is a schematic and partial top view of the lateral waveguide 32 according to another embodiment. In this example, it features a tapered coupler. Indeed, the width of edge 32.2 passes here from an initial value liae,init to a value of zero. This variation of the width is adiabatic so that the optical mode passes entirely from the lateral waveguide 32 into the saturable absorbing section 13. Thus, the tip coupler is located in the coupling zone zciae / sA, so that the width of the lateral waveguide 32 decreases to a value of zero liae / sA- The coupling zone zciae / SA corresponds approximately to the vertical overlap zone between the saturable absorbing section 13 and the tip coupler.

[0088] Figures 6A to 6C illustrate schematic and partial views of a pulsed laser device 1 according to an alternative embodiment. Here, the semiconductor medium 11 comprises, arranged longitudinally along the longitudinal axis X, a first gain section 12, a saturable absorbing section 13, and a second gain section 12. In this example, the vertical spacing dL / ms is equal to diae / sA and to diai / G.

[0089] These sections 12, 13 are not physically separated from each other, but on the contrary form areas of the same semiconductor pad. Electrical isolation between the sections two by two is achieved here by a notch 14 located at the interface between the saturable absorbing section 13 and each of the gain sections 12, at which appropriate doping is carried out, for example by implanting H+ protons.

[0090] As mentioned previously, the length along the X axis of the saturable absorbing section 13 is preferably less than the cumulative length of the gain sections 12, and is preferably on the order of 2 to 10% of this cumulative length of the gain sections 12. The saturable absorbing section 13 thus has a short saturation / desaturation time, suitable for the emission of short-duration laser pulses.

[0091] Furthermore, the semiconductor medium 11 may comprise a plurality of electrically isolated sections, each connected to an electrical bias source. The sign of the electrical voltage applied to each section can determine whether the section in question is a gain section 12 or a saturable absorbing section 13. In addition, the magnitude of the applied electrical voltage can correspond to the weight Wi applied to the synaptic inhibition or excitation signal.

[0092] Note that the optical coupling between the longitudinal waveguide 21 and the semiconductor medium 11 is here a supermode coupling (a type of optical coupling found in DFB lasers) insofar as the longitudinal waveguide 21 extends continuously under the semiconductor medium 11. In contrast, the lateral waveguide 32 has a coupler at its tip, so that the guided mode gradually passes from the waveguide 32 into the saturable absorbing section 13 (a type of optical coupling (which is found in DBR lasers). This can also be the case for the lateral waveguide 42 (not shown here).

[0093] The longitudinal waveguide 21 has a width lL / ms of its edge 21.2 in the coupling zone with the semiconductor medium 11. Preferably, the base 21.1 has a larger width in this coupling zone, which can help to reduce the confinement factor rL / ms.

[0094] The lateral waveguide 32 here has a peak coupler, so that its width liæ / sA decreases in the coupling region to a value of zero. Preferably, the base 32.1 has a width that also decreases in the coupling region, here also to a value of zero, which helps to increase the confinement factor Eiae / sA-

[0095] In view of what has been explained above, the operation of the triggering of the laser source 10 can be summarized by the table below, depending on whether the saturable absorbing section 13 is illuminated or not by an optical excitation pulse, and depending on whether the laser source 10 is in an excitability regime or not: Outside the excitability regime: g < gexc Excitability regime: gexc — g — gmax Excitation: emission of an excitation pulse Optical losses amin < a < amax No saturation => Intermediate state No laser pulse Optical losses a < amin Saturation => Conducting state Laser pulse emission No excitation: no emission of an excitation pulse Optical losses amax < a Blocking state No laser pulse Optical losses amax < a Blocking state No laser pulse

[0096] It is understood that the non-excitability regime of the laser source 10 corresponds in particular to two situations. The first situation corresponds to the refractory period: the gain, under the effect of the pump current, increases, but has not yet reached a value denoted gexc. In this case, the gain is not sufficient to participate, with the excitation optical pulse, in saturating the saturable absorbing section 13 and thus enabling the emission of a laser pulse. The second situation corresponds to inhibition: the refractory period is over, but the inhibition optical pulse causes a decrease in the gain, which falls below the value gexc and thus causes a departure from the excitability regime. Here too, the gain is no longer sufficient to participate in saturating the saturable absorbing section 13 and thus enabling the emission of the laser pulse.

[0097] This behavior of physiological neurons is thus observed in terms of excitability and refractory period. The neuron remains at rest when it is not excited. It does not emit a signal when it is in the refractory period (following the emission of a signal), and can emit a signal when it has exited the refractory period and is excited by signals of sufficient intensity. The operation of such a pulsed laser device 1 is described in patent application FR3123163 AL

[0098] Thus, the pulsed laser device 1 according to the invention comprises a hybrid III-V type laser source on Si and is actively triggered in an 'all-optical' manner. It effectively reproduces the excitability and refractory period properties of physiological neurons. The synaptic excitability and inhibition signals are optical pulses transmitted directly to sections 12, 13 of the semiconductor medium 11 of the laser source 10, without any O / E conversion. This is made possible by the hybrid configuration of the laser source 10, where the lateral waveguides 32, 42 are integrated into the photonic substrate 20 without being optically coupled to the optical cavity. This avoids the drawbacks of prior art 'O / E / O' type photonic artificial neurons, in particular those related to O / E conversion and the presence of photodiodes.This also avoids the drawbacks of prior art 'all-optical' photonic neurons, such as those related to the need to invert the pulses at the input of the photonic neuron and those related to the strict control of the frequency gap between the master and slave lasers. Furthermore, by choosing the widths of the integrated waveguides, the confinement factor of the optical modes is optimized, which improves the performance of the pulsed laser device.

[0099] Specific embodiments have just been described. Various variants and modifications will be apparent to those skilled in the art.

Claims

1. Demands Pulsed laser device (1), comprising: • a pulsed, hybrid III-V silicon-based laser source (10) comprising: • a semiconductor medium (11) comprising quantum wells, made from a III-V compound, located in an optical cavity defining a longitudinal axis (X), and comprising at least one gain section (12) and at least one saturable absorbing section (13) where the quantum wells are coplanar; • a photonic substrate (20), made of silicon, on which the semiconductor medium (11) rests, and in which is located a longitudinal waveguide (21) participating in defining the optical cavity and optically coupled to the semiconductor medium (11) along the longitudinal axis (X), the longitudinal waveguide (21) having a width lL / ms and a vertical spacing dl / m, vis-à-vis the semiconductor medium (11), in a coupling zone zcL / ms with the semiconductor medium (11), predefined so that the optical mode propagating in the longitudinal waveguide (21) has a confinement factor rL / ms in the quantum wells of the semiconductor medium (11); • at least one optical control device (30; 40), comprising: • at least one emitting source (31; 41) adapted to emit at least one optical control pulse of predefined intensity; • at least one lateral waveguide (32; 42), - located in the photonic substrate (20), - optically coupled to the saturable absorbing section (13) or to the gain section (12) to transmit the optical control pulse, in a

2.

3.

4.

5. inclined with respect to the longitudinal axis (X) to avoid optical coupling with the optical cavity, and - having a width (liæ / sA ; ki / c) and a vertical spacing (diae / sA; diai / G) with respect to the semiconductor medium (11), in a coupling zone (zciae / sA ; zciai / G) with said corresponding section (13 ; 12), predefined such that the optical mode propagating in the lateral waveguide (32 ; 42) has a confinement factor (riae / SA ; Tiai / c) in the quantum wells of said corresponding section (13 ; 12) greater than rL / ms. Pulsed laser device (1) according to claim 1, wherein the longitudinal waveguide (21) has a width lL / ms in its coupling zone zcL / ms, and the lateral waveguide (32; 42) has a width (liae / SA; U / g) in its coupling zone (zciae / SA; zciai / G) less than lL / ms. Pulsed laser device (1) according to claim 1 or 2, wherein the longitudinal waveguide (21) has a vertical spacing dL / ms in its coupling zone zcL / ms with respect to the quantum wells of the semiconductor medium (11), and the lateral waveguide (32) has a vertical spacing (diae / SA ; diai / G) in its coupling zone (zciae / sA ; zC]ai / G) with respect to the quantum wells of the semiconductor medium (11), where the vertical spacing dL / ms is greater than or equal to that of the lateral waveguide (32 ; 42). Pulsed laser device (1) according to any one of claims 1 to 3, wherein the longitudinal waveguide (21) and the lateral waveguide (32) are edge waveguides formed of a base (21.1; 32.1) and an edge (21.2; 32.2), the lower face (21.1; 32.1) of the longitudinal waveguide (21) and that of the lateral waveguide (32) being coplanar. Pulsed laser device (1) according to any one of claims 1 to 4, wherein the longitudinal waveguide (21) extends continuously under the semiconductor medium (11).

6. Pulsed laser device (1) according to any one of claims 1 to 5, wherein the side waveguide (32; 42) extends continuously under the corresponding section (13; 12) or comprises at least one tip coupler.

7. Pulsed laser device (1) according to any one of claims 1 to 6, wherein the semiconductor medium (11) comprises at least two gain sections (12) located on either side of the saturable absorbing section (13).

8. Pulsed laser device (1) according to any one of claims 1 to 7, wherein the gain section (12) and the saturable absorbing section (13) are physically distant portions of each other, or are areas of the same plot formed by the semiconductor medium (11).

9. Pulsed laser device (1) according to any one of claims 1 to 8, wherein at least one optical control device is an optical excitation device (30), the emitting source (31) being adapted to emit at least one optical excitation pulse of predefined intensity, and the lateral waveguide (32), referred to as the excitation waveguide, is optically coupled to the saturable absorbing section (13), the optical mode propagating in the lateral waveguide (32) of excitation then exhibiting a confinement factor Tiae / sA in the quantum wells of the saturable absorbing section greater than rL / ms.

10. Pulsed laser device (1) according to any one of claims 1 to 8, wherein at least one optical control device is an optical inhibition device (40), the emitting source (41) being adapted to emit at least one optical inhibition pulse of predefined intensity, and the lateral waveguide (42), referred to as the inhibition waveguide, is optically coupled to the gain section (12), the optical mode propagating in the lateral inhibition waveguide (42) then exhibiting a confinement factor riai / G in the quantum wells of the gain section greater than rL / ms.

11. Pulsed laser device (1) according to claims 9 and 10, comprising an optical excitation device (30) and an optical inhibition device (40).

12. Pulsed laser device (1) according to claim 11, comprising optical intensity attenuators (2) arranged on the lateral waveguides (32, 42), and adapted to decrease the intensity of optical excitation and inhibition pulses.

13. Photonic artificial neural network, comprising a plurality of pulsed laser devices according to claim 11 or 12, wherein each pulsed laser source (10) forms a photonic artificial neuron, the photonic artificial neurons being optically connected to each other.

14. Photonic artificial neural network according to claim 13, wherein a longitudinal waveguide (21) of a pulsed laser device forms a lateral excitation or inhibition waveguide of another pulsed laser device.

15. A method of using a pulsed laser device (1) according to any one of claims 11 or 12, comprising the following steps: • forward biasing of the gain section (12) by an electric current of a predefined constant intensity such that the gain g of the semiconductor medium (11) reaches a maximum value gmax, and application of a zero or reverse bias to the saturable absorbing section (13); • emission of an optical excitation pulse by the optical excitation device (30), causing emission of a laser pulse by the pulsed laser source (10) if the gain is at least equal to an excitability value gexc; • emission of an optical inhibition pulse by the optical inhibition device (40), preventing the emission of a laser pulse by a decrease in the value of the gain below the excitability value gexc.

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