Photonic circuit for generating squeezed light, and corresponding manufacturing process

Abstract

The present invention relates to a photonic circuit for generating squeezed light, comprising: an electron-pumping source (SPS) that pumps electrons at a constant rate, a distributed optical-feedback quantum dot laser component (QDL), the laser component being electrically coupled to the silent pump and integrated into a semiconductor substrate, the laser component having a predefined threshold current. The silent pump is configured to inject, into the laser component, a supply current with an intensity proportional to the intensity of the predefined threshold current by a factor between 1 and 5, so as to make the laser component generate a phase-squeezed or amplitude-squeezed light beam.

Description

[0001] Photonic circuit for generating compressed light and corresponding manufacturing process

[0002] technical field

[0003] The invention falls within the field of quantum photonics technologies.

[0004] The invention relates, more particularly, to a photonic circuit designed to generate compressed states of light (called "squeezed states"). Such states of light exhibit optimal quantum noise characteristics, that is, a quantum noise level lower than the classical limit established by laser light.

[0005] The invention has many applications, including, but not limited to, high-precision metrology and information and communication technologies.

[0006] Technological background

[0007] Quantum technologies are poised to revolutionize the future of many technologies, particularly in the field of the Internet by enabling significantly faster and more secure data transmissions thanks to new quantum encryption protocols, and also in the field of metrology where the search for compressed states of light is driven by the possibility of making measurements exceeding standard limits of precision. These limits are intimately linked to quantum fluctuations in the intensity of laser light.

[0008] All these applications nevertheless require the use of increasingly powerful laser sources in order to perform ever more complex operations and enable high-speed, secure and low-energy communications.

[0009] As with all detectors, the sensitivity of gravitational wave detectors is strongly affected by the signal-to-noise ratio. Noise reduction is therefore a central issue for improving the signal-to-noise ratio and thus the performance of gravitational wave detectors. While designers make great efforts to reduce noise, conventional optical measurement methods are ultimately subject to limited sensitivity due to the intrinsic shot noise carried by laser light. The quantum limit is therefore generally treated as a fundamental constraint, and numerous scientific experiments have been conducted to demonstrate that squeezed states can be exploited to measure signals below the shot noise level, particularly for gravitational wave detection, in order to extend the detection range of laser interferometric detectors.Compressed states are essential for 6G technology, offering enormous potential for faster, more secure, and more precise communications, as well as significant advances in sensors and sensing. These states also find numerous applications in quantum teleportation, quantum computing, coding for quantum error correction, and inertial sensors (gyroscopes, accelerometers, magnetometers). Recently, compressed light sources have become crucial for quantum state engineering, particularly for generating and amplifying non-Gaussian states using the photon subtraction method, which is necessary for various quantum processing protocols. An example of a quantum repeater known from the prior art is presented in the article "Quantum repeater using twomode squeezed states and atomic noiseless amplifiers" by Anders JE Bjerrum et al., Phys. Rev. A 107, 042606 - 12 April 2023.More recently, novel LNOI (Lithium Niobate On Insulators) photonic platforms have been designed and are generating considerable interest in the scientific community due to their unprecedented electro-optical and nonlinear properties. Recent nanofabrication technologies have further broadened the range of applications, enabling the production of modular structures integrating photonic circuits and / or LiNbOs waveguides for generating compressed states. Finally, compressed light holds great potential in biology for improving imaging resolution, increasing the sensitivity of biomolecule detection, and enhancing real-time fluorescence microscopy.

[0010] It is known that the noise level depends on the laser parameters, particularly the amplitude uncertainty and the phase uncertainty. A compressed (or "squeezed") state is a specific state of laser light where at least one of the uncertainty levels (amplitude or phase) can be reduced in such a way as to reduce quantum noise over a given wavelength or range of wavelengths.

[0011] It is known in the prior art to produce compressed states with laser light using optical devices operating on nonlinear interaction processes (parametric conversion). An example of such an optical device is illustrated in the publication by T. Kashiwazaki et al. entitled "Over-8-dB squeezed light generation by a broadband waveguide optical parametric amplifier toward fault-tolerant ultra-fast quantum computers" Appl. Phys. Lett. 122, 234003 (2023). Although the level of state compression can reach several tens of decibels, these devices are relatively complex to implement and require bulky optics that are not compatible with integration on photonic circuits. It is also known to use nonlinear coupling effects with atomic lasers to produce compressed states.However, the compression effect appears to have little stability and is complex to implement in practice.

[0012] There is therefore a real need to provide a compact and efficient device capable of reaching a quantum operating regime characterized by the production of at least one compressed state of light.

[0013] Description of the invention

[0014] In a particular embodiment of the invention, a compressed light generation photonic circuit is proposed, comprising a constant-flow electron pumping source, referred to as a silent pump, and a quantum dot laser component. The laser component is electrically coupled to the silent pump and integrated into a semiconductor substrate. The laser component has a predefined threshold current. Such a circuit is characterized in that the silent pump is configured to inject into the laser component a supply current whose intensity is proportional to the intensity of the predefined threshold current by a factor of between 1 and 5, so as to cause the laser component to generate a light beam in at least one compressed state of light.

[0015] The general principle of the invention is based on the use of on-chip integrated quantum dot laser components and constant-rate electron pumping to generate compressed states of light. This approach makes it possible to provide an on-chip integrated photonic source operating below the standard quantum limit.

[0016] More specifically, said laser component comprises a stack of layers based on semiconductor materials, said stack comprising: a lower optical confinement layer extending over the semiconductor substrate; an active layer extending over the first confinement layer, said active layer incorporating at least one plane of quantum dots; a structured layer extending over the active layer; an upper optical confinement layer extending over the structured layer.

[0017] The use of semiconductor materials, particularly among the III-V compounds of the periodic table of elements, gives the photonic circuit properties of insensitivity to parasitic optical feedback, increased thermal stability, and better bandwidths at room temperature.

[0018] According to a particular implementation, the active layer has a length of at least 500 pm. Such a characteristic guarantees a quantum noise level lower than the classical limit established by laser light.

[0019] According to a particular implementation, the number of quantum dot planes contained in the active layer is between 1 and 2. Such a number of planes is particularly well suited to use at very low temperatures (typically cryogenic temperatures).

[0020] According to one implementation variant, the number of quantum dot planes contained in the active layer is between 3 and 8, and more specifically between 3 and 5. Such a number of planes is particularly well suited for use at room temperature.

[0021] According to a particular implementation, said at least one quantum dot plane has a quantum dot density of between 100 dots / pm 2 and 1000 boxes / pm 2 Such a density of quantum dots allows the laser component to reach a quantum operating regime.

[0022] In a particular implementation, the layer stack comprises: on the back side, a high-reflectivity mirror with a reflection coefficient greater than 95% at the laser emission wavelength, and on the front side, a partial-reflectivity mirror with a reflection coefficient greater than 32% at the laser emission wavelength and less than or equal to the reflection coefficient of the high-reflectivity mirror. Such a reflectivity profile ensures the generation of a reduced number of photons, allowing the laser component to achieve the desired quantum operating regime. This is particularly pronounced with longer active layers (greater than 500 pm).

[0023] According to a particular configuration, the structured layer forms a distributed Bragg reflector sized to cause said at least one laser component to deliver a single-mode light beam and in which a first metallic contact extends over the upper optical confinement layer and a second metallic contact extends over the surface of the semiconductor substrate.

[0024] This initial stacking configuration causes the laser component to generate a single-mode light beam in at least one compressed state of light, based on distributed optical feedback operation. The distributed Bragg reflector is formed by a periodic array of lateral corrugations of predefined period, extending along the propagation axis of the laser emission.

[0025] In another specific configuration, the structured layer forms a Fabry-Perot cavity sized to enable at least one laser component to deliver a multimode light beam. In this cavity, a first metallic contact extends across the upper optical confinement layer, a second metallic contact extends across the surface of the semiconductor substrate, and a third contact, called a saturable absorbing contact, extends across the upper optical confinement layer. This saturable absorbing contact is designed to receive a negative electrical voltage. This second stacking configuration enables the laser component to generate a multimode light beam in which each mode (or wavelength) exhibits at least one compressed state of light.

[0026] In another embodiment of the invention, a method for generating compressed light is proposed using a photonic circuit comprising a constant-flow electron pumping source, referred to as a silent pump, and a distributed-feedback quantum dot laser component electrically coupled to said silent pump, the laser component having a predefined laser threshold current. Such a method is characterized in that it includes a step of injecting into the laser component a supply current whose intensity is proportional to the intensity of the laser threshold current, by a factor between 1 and 5, so as to cause the laser component to generate a light beam in at least one compressed state of light.

[0027] In another embodiment of the invention, a photonic device is proposed implementing a compressed light generation sound circuit as described above in any one of its implementations. Various uses of the aforementioned device are possible, including (but not limited to):

[0028] - for the realization of quantum sensors / detectors (gyroscopes, accelerometers, interferometers, etc.);

[0029] - for the development of quantum telecommunications equipment (optical computers, quantum communication circuits and components on-chip, quantum encoders, quantum repeaters, LNOI chips, etc.)

[0030] - for the production of medical instruments / devices (medical imaging devices, biosensors, etc.)

[0031] List of figures

[0032] Other features and advantages of the invention will become apparent from the following description, given by way of illustrative and non-limiting example, and the accompanying drawings, in which:

[0033] - Figure 1 illustrates a schematic diagram of a photonic circuit for generating compressed light according to a first embodiment of the invention;

[0034] - Figure 2 represents a perspective view of a quantum dot laser component integrated into the photonics circuit according to the first embodiment;

[0035] - Figure 3 illustrates a schematic diagram of a photonic circuit for generating compressed light according to a second embodiment of the invention;

[0036] - Figure 4 represents a perspective view of a quantum dot laser component integrated into the photonics circuit according to the second embodiment.

[0037] Detailed description of the invention

[0038] In all figures in this document, identical elements and steps are designated by the same numerical reference.

[0039] The general principle of the invention is based on the use of on-chip integrated quantum dot laser components and constant-rate electron pumping to produce compressed states of laser light. This approach makes it possible to provide an on-chip integrated photonic source exhibiting a quantum operating regime.

[0040] Two specific photonic circuit implementations for generating compressed laser light are presented below: a single-mode quantum dot laser light source and a mode-locked quantum dot laser light source. The first implementation is described below with reference to Figures 1 and 2, and the second is described subsequently with reference to Figures 3 and 4.

[0041] Figure 1 shows, in schematic block form, a photonic circuit SLG according to a particular embodiment of the invention. In this particular embodiment, the photonic circuit SLG is configured to generate compressed light. Such a circuit comprises a constant-rate electron pumping source SPS, a quantum dot laser component QDL electrically coupled to the pumping source SPS (for example, by means of an electrical cable EG), and an attenuator component ATT optically connected to the output of the QDL laser component (for example, by means of an optical waveguide WG). The quantum dot laser component QDL, the waveguide WG, and the attenuator component ATT are integrated on a chip P, for example, made from a silicon or GaAs substrate. The attenuator ATT controls the output power of the QDL laser component according to the application.

[0042] The SPS pump source, also commonly called a "quiet pump," is a high-impedance electronic pump source that allows for the periodic injection of electrons at a constant rate into the QDL laser component. This periodic electron injection is illustrated by black dots in the figure. The SPS pump source is also characterized by its supply current, the intensity of which is chosen according to the laser current threshold of the QDL component. It is worth recalling that every laser component has a threshold current, or characteristic current threshold, beyond which it emits laser light.

[0043] The inventors of the present invention have surprisingly discovered that the use of a distributed feedback type quantum dot laser component, powered by a silent pump with a supply current of intensity proportional to the intensity of the threshold current of the laser component by a factor between 1 and 5, makes it possible to cause the laser component to generate a light beam in at least one compressed state of light, making the SLG photonic circuit a quantum light source.

[0044] For example, with a laser threshold current of 10 mA and an operating range of the silent pump between 10 and 100 mA, a supply current between 10 and 50 mA can be applied to the QDL laser component by the SPS pump to generate compressed light (for use of the laser chip at room temperature). The compressed light thus exhibits a particular quantum state where the amplitude uncertainty or the phase uncertainty is reduced to below the standard quantum noise level: this is referred to as an amplitude-compressed (or intensity-compressed) state or a phase-compressed state. Other laser threshold current and operating range values ​​can, of course, be considered without departing from the scope of the invention, depending on the opto-geometric profile chosen for the laser component.

[0045] Figure 2 illustrates an example of a quantum dot laser component used in the SLG photonic circuit. In this particular embodiment, the QDL laser component comprises a stack of layers based on semiconductor materials: a lower optical confinement layer 110, for example based on n-doped AlGaAs on GaAs, extending over the silicon substrate 100; an active layer 120 extending over the first confinement layer 110, said active layer incorporating several planes of quantum dots; a structured layer 130 extending over the active layer; an upper optical confinement layer 140, for example based on p-doped AlGaAs on GaAs, extending over the structured layer 130; a first metallic contact 150 extending over the optical confinement layer 140 and a second metallic contact 160 extending on the surface of the silicon substrate 100 and at a distance from the layers 110, 120, 130 and 140.

[0046] The active layer 120 of the QDL laser component is characterized in particular by its structural dimensions, the number of planes and the density of the quantum dots it contains, as well as the materials from which it is composed. It has been shown that an active layer with a length L of at least 500 pm (typically 1000 pm or 2000 pm) makes it possible to guarantee a quantum noise level below the classical limit established by laser light.

[0047] A number of quantum dot planes between 3 and 5, and more generally between 3 and 8, is particularly well-suited for room-temperature use. Note that a smaller number, typically 1 to 2 quantum dot planes, is sufficient for use at very low temperatures (cryogenic temperatures). Quantum dots are semiconductor nanocrystals with three-dimensional quantum confinement. They can be of the InAs / InGaAs type, meaning they are InAs nanocrystals arranged in an InGaAs matrix. The active layer can therefore consist of several InGaAs thin layers, each containing several InAs nanocrystals. The average size of quantum dots is between 0.5 nm and 50 nm, for example, between 1 nm and 20 nm. The average density of quantum dots per plane is between 100 dots / pm 2 and 1000 boxes / pm 2This allows the QDL laser component to reach its quantum operating regime. InAs / GaAs quantum dots represent an interesting class of nanostructures for the realization of high-performance, integrable, compressed-state light generators on silicon chips. Thanks to their discrete energy levels, such components exhibit thermal stability and insensitivity to optical feedback, enabling integration in a silicon environment without optical isolators.

[0048] Quantum dot designs are obtained using a molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD) growing technique, compatible with classical technologies in the field of integrated photonics.

[0049] The ends of the layer stack are made up of HR and AR mirrors which define the optical cavity of the laser: on the back face, a high reflectivity (HR) mirror whose reflection coefficient is greater than 95% at the laser emission wavelength, and on the front face, a partial reflectivity (AR) mirror whose reflection coefficient is greater than 32% at the laser emission wavelength and less than or equal to the value of the reflection coefficient of the high reflectivity mirror.

[0050] Such a reflectivity profile ensures the generation of a reduced number of photons, allowing the laser component to reach the desired quantum operating regime. This is particularly pronounced when the length L of the active layer is greater than 500 pm. The front and back faces of the stack can be obtained by cleaving. The other lateral faces are inactive. The reflectivities of the mirrors are primarily determined by the refractive index of the structure. The reflection coefficient can be adjusted by applying a single or multilayer dielectric and / or metallic coating to at least one of these active faces of the stack. This coating also provides protection for the treated face(s).

[0051] The structured layer 130 is shaped to form a distributed Bragg reflector, sized to enable the QDL laser component to deliver a single-mode beam at 1.55 pm, based on distributed feedback laser operation. The Bragg reflector is formed by a periodic array of lateral corrugations of predefined period, extending along the laser emission propagation axis. The role of the array is to ensure periodic modulation of the real or imaginary part of the effective index of the active layer of the stack, thereby obtaining the selective feedback condition around the Bragg condition that ensures single-mode laser operation.

[0052] The first contact 150 is electrically connected to the SPS source and intended to receive a supply current of a few tens of mA and the second contact 160 is electrically connected to ground.

[0053] Figure 3 presents, in schematic block form, an SLG2 photonic circuit according to another particular embodiment of the invention. In this second embodiment, as with the SLG circuit, the SLG2 photonic circuit is configured to generate compressed light, but based on mode-locked operation. The main difference from the SLG circuit lies in the nature of the structured layer of which the laser component is composed and the addition of a saturable absorbing electrical contact on it.The SLG2 photonic circuit comprises, in particular, a constant-rate electron pumping source SPS2, a quantum dot laser component QDL2 electrically coupled to the SPS2 pumping source, an attenuator component ATT2 optically connected to the output of the QDL laser component (for example, via an optical waveguide WG2), an amplitude modulator component AM optically connected to the output of the attenuator ATT2, and a phase modulator component PM optically connected to the output of the phase modulator PM. The QDL2, ATT, AM, and PM components, as well as the optical waveguides connecting them, are integrated onto a silicon chip P2.

[0054] The operation of the SPS2 calm pump is identical to that of the SPS calm pump in the first embodiment (whose operation is detailed above in relation to Figure 1). It is configured to perform periodic injection of electrons at a constant flow rate into the QDL2 laser component with a supply current whose intensity is chosen according to the laser current threshold of the QDL2 component. To enable the generation of phase- or amplitude-compressed light, the SPS2 calm pump supplies the QDL2 component with a pump signal whose supply current is fixed to be proportional to the laser component's threshold current intensity by a factor between 1 and 5.

[0055] Figure 4 illustrates an example of a quantum dot laser component used in the SLG2 photonic circuit. In this particular embodiment, the QDL2 laser component comprises a stack of layers based on semiconductor materials: a lower optical confinement layer 210, for example based on n-doped AlGaAs on GaAs, extending over the silicon substrate 200; an active layer 220 extending over the first confinement layer 210, said active layer integrating several planes of InAs / InGaAs-based quantum dots; a structured layer 230 extending over the active layer 220; an upper optical confinement layer 240, for example based on n-doped AlGaAs on GaAs, extending over the structured layer 230;a first metallic contact 250 extending partially over the optical confinement layer 240 in the rear part of the component (intended to receive a positive voltage) and a second metallic contact 270 extending partially over the optical confinement layer 240 in the front part of the component and at a distance from the first contact 250; a third metallic contact 260 extending on the surface of the substrate 200 and at a distance from the layers 110, 120, 130 and 140.;

[0056] The active layer 120 of the QDL2 laser component is characterized in particular by its structural dimensions, the number of planes and the density of the quantum dots it comprises, as well as the materials that compose it, as discussed above in relation to Figure 2. The active layer 120 is formed for example of InAs quantum islands deposited in InGaAs quantum wells.

[0057] The ends of the layer stack are made up of HR2 and AR2 mirrors which define the optical cavity of the laser: on the back face, a high reflectivity mirror (HR2) whose reflection coefficient is greater than 95% at the laser emission wavelength, and on the front face, a partial reflectivity mirror (AR2) whose reflection coefficient is greater than 32% at the laser emission wavelength and less than or equal to the value of the reflection coefficient of the high reflectivity mirror.

[0058] The structured layer 230 is shaped to form a Fabry-Perot cavity sized to cause said at least one laser component to deliver a multimode light beam.

[0059] The first contact, 250, is electrically connected to the SPS source and designed to receive a supply current of a few tens of mA. The second contact, 260, is electrically connected to ground. The second contact, 270, is a saturable absorbing contact designed to receive a negative DC voltage, typically between 0 and 8 V. The combined use of the Fabry-Perot cavity and the electrode array, including the saturable absorbing contact 270, enables the generation of a highly coherent optical frequency comb (multimode behavior), with each row of the comb exhibiting a compressed state. In other words, this particular configuration allows the QDL2 laser component to generate a multimode light beam in which each mode (or wavelength) exhibits a compressed state (in phase or amplitude).

[0060] The QDL and QDL2 laser components described above, respectively in relation to Figures 2 and 4, each have a structure generally shaped like a parallelepiped bar. Naturally, the materials used, the geometry, and the structural dimensions of the laser component according to the invention can be adapted on a case-by-case basis, particularly depending on the applications and optical performance requirements. Other embodiments of the invention can thus be considered without departing from the scope of the invention. For example, one could integrate a quantum dot laser component with an annular guiding structure onto a photonic circuit to achieve a more compact design (without compromising the optical performance of the compressed light source).

Claims

DEMANDS 1. Photonic circuit for generating compressed light, characterized in that it comprises a constant electron flow pumping (SPS) source, called a silent pump, a quantum dot laser (QDL) component, the laser component being electrically coupled to said silent pump and integrated into a semiconductor substrate, the laser component having a predefined threshold current, said silent pump being configured to inject, into the laser component, a supply current of intensity proportional to the intensity of the predefined threshold current by a factor between 1 and 5, so as to cause the laser component to generate a light beam in at least one compressed state of light.

2. Photonic circuit according to claim 1, wherein said laser component (QDL) comprises a stack of layers based on semiconductor materials, said stack comprising: a lower optical confinement layer (110) extending over the semiconductor substrate; an active layer (120) extending over the first confinement layer, said active layer integrating at least one plane of quantum dots; a structured layer (130) extending over the active layer; an upper optical confinement layer (140) extending over the structured layer.

3. Photonic circuit according to claim 2, wherein the active layer has a length (L) of at least 500 pm 4. Photonic circuit according to any one of claims 2 and 3, wherein the number of quantum dot planes contained in the active layer is between 1 and 2.

5. Photonic circuit according to any one of claims 2 to 4, wherein the number of quantum dot planes contained in the active layer is between 3 and 8, and more particularly between 3 and 5.

6. A photonic circuit according to any one of claims 2 to 5, wherein said at least one quantum dot plane has a quantum dot density of between 100 dots / pm 2 and 1000 boxes / pm 2 .

7. Photonic circuit according to any one of claims 2 to 6, wherein said layer stacking comprises: on the back face, a high reflectivity (HR) mirror having a reflection coefficient greater than 95% at the laser emission wavelength, and on the front face, a partial reflectivity (AR) mirror having a reflection coefficient greater than 32% at the laser emission wavelength and less than or equal to the value of the reflection coefficient of the high reflectivity mirror.

8. Photonic circuit according to any one of claims 2 to 7, wherein the structured layer forms a distributed Bragg reflector dimensioned to cause said at least one laser component to deliver a single-mode light beam and wherein a first metallic contact (150) extends over the upper optical confinement layer and a second metallic contact (160) extends over the surface of the semiconductor substrate.

9. Photonic circuit according to any one of claims 2 to 7, wherein the structured layer forms a Fabry-Perot cavity dimensioned to cause said at least one laser component to deliver a multimode light beam and wherein a first metallic contact (250) extends over the upper optical confinement layer, a second metallic contact (260) extends over the surface of the semiconductor substrate and a third contact (270), said saturable absorbing contact, extends over the upper optical confinement layer, said saturable absorbing contact being intended to receive a negative electrical voltage.

10. A method for generating compressed light by means of a photonic circuit comprising a constant-flow electron pumping source (QPS), referred to as a silent pump, and a quantum dot laser (QDL) component, of the distributed feedback type, electrically coupled to said silent pump, the laser component having a predefined laser threshold current, the method being characterized in that it comprises a step of injecting, into the laser component, a supply current of intensity proportional to the intensity of the laser threshold current, by a factor between 1 and 5, so as to cause the laser component to generate a light beam in at least one compressed state of light.

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