DE102020131012A1 - PHOTONIC NETWORK - Google Patents

Abstract

A photonic network comprises: a multiplicity of optical waveguides (13) running parallel to one another, each waveguide (13) having an optical input (15) and an optical output (17), and a multiplicity of optoelectronic light sources (19), in particular Laser light sources, preferably laser diodes, wherein each optical input (15) of the waveguides (13) is coupled to a light source (19) for feeding light into the respective waveguide (13), and wherein the waveguides (13) and the light sources (19) are formed monolithically in a material system.

Description

The present invention relates to a photonic network, in particular a photonic neural network.

Artificial neural networks can be seen as key elements for current and future technologies, such as machine learning. The production of artificial neural networks with standard IT hardware components is difficult to implement, and such networks require very high computing power.

Another approach is optical neural networks. It is known to combine semiconductor lasers with an optical waveguide network fabricated on a silicon substrate to produce a photonic network.

It is an object of the present invention to provide an improved photonic network which, in particular, can also be produced in a simple manner.

The object is achieved by a photonic network having the features of claim 1. Preferred embodiments and developments of the invention are specified in the dependent claims.

A photonic network according to the invention, in particular a photonic, artificial neural network, comprises a multiplicity of optical waveguides running parallel to one another, each waveguide having an optical input and an optical output, and a multiplicity of optoelectronic light sources, in particular laser light sources, preferably laser diodes, each optical input of the waveguide is coupled to a light source for feeding light into the respective waveguide, wherein the waveguide and the light sources are monolithic in a material system.

In the case of the photonic network according to the invention, at least the light sources and the waveguides are monolithically integrated in a material system. As a result, the photonic network can be produced in a relatively simple and very compact manner. In addition, a high packing density of the elements of the network can be achieved. The waveguide structures, the light sources and possibly other elements can be arranged in large numbers in a small volume.

The material system of the light sources and the waveguide is preferably the same, at least in the area of the light-generating and light-conducting layers. The material system is preferably an indium aluminum gallium arsenide InAlGaAs material system.

A light source can be coupled to a respective optical input of an associated waveguide in such a way that one or more light-generating or light-guiding layers of the light source lie in the same plane as one or more light-guiding layers of the waveguide. A direct coupling of the light from the light source into the associated waveguide is possible as a result. In addition, an at least essentially identical band structure with an essentially equally large band gap can result for the light-guiding layers of the waveguides and the light sources. A band gap in the waveguides is preferably slightly enlarged, as will be explained below, in order to avoid absorption of the light provided by the light source, in particular in the form of laser pulses.

In the material system, the waveguides can be designed at least in sections as quantum well waveguides, with each waveguide having at least one or more quantum wells. In particular, the one or more light-guiding layers of the waveguide can be designed in such a way that they form one or more quantum wells. A high integration density can be achieved by using such waveguides.

Preferably, the quantum well(s) of the quantum well waveguides have a bandgap that corresponds to an energy difference that is greater than the energy of the photons emitted by the light sources. The band gap refers to the energetic distance between the conduction and valence bands in the respective quantum well. Since the band gap is larger than the energy of the photons from the light source, absorption of the photons in the waveguides can be avoided or at least reduced.

It can be provided, in particular to generate such a band gap, that the quantum well or the quantum wells of the quantum well waveguide is or are produced by means of a quantum well mixing method. Such a method, which is known per se, is also called quantum well intermixing. Quantum well intermixing is a technique that can be used to modify the band gap of a quantum structure. The modified quantized energy state mostly leads to a blue shift of the band gap and therefore to a widening of the band gap.

In the material system, the waveguides can have a higher optical refractive index than regions of the material system adjoining the waveguides. Light guiding along the waveguides based on the effect of total internal reflection can thereby be achieved.

The difference between the optical refractive indices of the waveguide and the adjacent regions can be in the hundredth or thousandth range. A refractive index difference of the order of a few thousandths can already be sufficient. For example, in an InAlGaAs material system, the optical index of refraction is about 3.5. For a waveguide with a refractive index of 3.501, the critical angle of total reflection is arcsin(3.5/3.501) = 88.6°. This means that bends with a radius of 6 µm would be possible for the waveguide.

In the material system, the waveguides can be compressed or tensioned at least in sections. As a result, the refractive index in the waveguides can be increased, in particular in the thousandths range.

At least one microring resonator can be formed in the material system between respectively adjacent waveguides. Thereby a coupling between the waveguides can be accomplished.

Microring resonators are known per se. Reference is made to the scientific publication by TAIT et al.: "Microring Weight Banks", IEEE Journal of Selected Topics in Quantum Electronics, Vol. 22, No. 6, Nov/Dec 2016, 5900214.

The microring resonator can have a control element which is provided for controlling the coupling out of light from one waveguide and for coupling the light into the adjacent waveguide. The control element can be switched between two states, in particular electrically switchable, wherein in a first state light is coupled from a waveguide into the microring resonator and is further coupled out from the microring resonator into the adjacent waveguide.

In at least one configuration of the invention, the optical refractive index of the microring resonator can be adjustable by means of the control element. The microring resonator can thereby be brought into resonance with the waveguides to achieve effective coupling between the waveguides.

In at least one configuration of the invention, at least one and preferably all waveguides can have at least one weighting element. The importance of a waveguide in the network can be set via the weighting element.

A respective waveguide cannot have any mixed quantum wells in the area of a weighting element. The band gap in the area of a weighting element can thus correspond in particular to the energy of the photons provided by the light source. Therefore, in a state of the weighting element, photons from the light source can be absorbed.

A respective weighting element can be brought into a state in which population inversion occurs. The weighting element is then transparent to the incoming light.

In particular, a respective weighting element can be continuously switchable between a first state and a second state, for example by means of an electrical signal, such as a voltage signal, which can be varied between 0 volt and 1 volt. In the first state, the weighting element completely absorbs incident light, while in the second state it is transparent to incident light. Partial absorption takes place in intermediate states between the first and second state, with the degree of absorption increasing the closer the set intermediate state is to the first state.

At least one and preferably all of the waveguides can have at least one pulsating element. Such elements are also referred to as "spiking neuron" or "firing neutron" in an artificial neural network.

A given waveguide cannot have mixed quantum wells in the region of a pulsating element. The band gap in the area of a pulsating element can thus correspond in particular to the energy of the photons provided by the light source.

A respective pulsating element may be capable of being brought into a state in which population inversion occurs. Incoming light can be amplified non-linearly, particularly strongly, so that non-linear behavior can be simulated.

In one configuration of the invention, a respective terminating element can be formed at each optical output of the waveguides in the material system. By means of the terminating elements, the output layer of a neural network works can be realized. The information processed in the network can be obtained or read out by means of the terminating elements.

A respective terminating element can be designed as a detector for detecting the light arriving at the respective optical output.

A respective waveguide cannot have any mixed quantum wells in the area of a terminating element. The semiconductor layers forming a terminating element can be in the form of photodiodes and can be subjected to a blocking voltage, so that the terminating elements can function as photodiodes from a functional point of view.

In addition to the light sources and the waveguides, one, several or all other elements of the network, in particular the microring resonators, the control elements, the weighting elements, the pulsating elements and/or the terminating elements can be formed monolithically in the material system.

The light source is in particular a laser diode. The light source can be operated in pulsed or continuous mode. Thus, when reference is made herein to light, incident light, or photons, a light pulse emitted by a light source may be associated therewith. Light does not necessarily have to be visible. Light can in particular also be in the infrared or in the ultraviolet spectral range.

• 1 zeigt schematisch ein Ausführungsbeispiel des erfindungsgemäßen photonischen Netzwerkes.

Exemplary embodiment variants of the invention are explained below in connection with representations in the figures.

• 1 shows schematically an embodiment of the photonic network according to the invention.

This in 1 The photonic network 11 shown comprises a multiplicity, here four, of optical waveguides 13 running parallel to one another. Each waveguide 13 has an optical input 15 and an optical output 17 . The network 11 also includes a large number, here four, of optoelectronic laser light sources 19, which are in particular laser diodes.

Each optical input 15 of the waveguide 13 is coupled to a light source 19, the light source 19 being provided for feeding light, in particular in the form of laser pulses, into the respective waveguide 13. The waveguides 13 and the light sources 19 are formed monolithically in the same material system.

The photonic network 11 also comprises microring resonators 21 between respective adjacent waveguides 13. In particular, in 1 Seen from top to bottom, between the uppermost, first and second waveguide 13, two micro-ring resonators 21 are arranged. A microring resonator 21 is provided between the second and third waveguides 13 . In turn, two microring resonators 21 are arranged between the third and bottom, fourth waveguide 13 .

Each microring resonator 21 has a control element 23 which is provided for controlling the coupling out of light from a waveguide 13 and for coupling the light into the adjacent waveguide 13 .

A weighting element 25 and a pulsating element 27, which is also referred to as “spiking neuron” or “firing neutron”, are integrated into each waveguide 13. In addition, a respective terminating element 29 is arranged at each optical output 17 of the waveguide 13 .

The elements mentioned, ie the microring resonators 21 with the control elements 23, the weighting elements 25, the pulsating elements 27 and the terminating elements 29 are also formed monolithically with the waveguide 13 and the light sources 19 in the material system. The material system is preferably an indium aluminum gallium arsenide (InAlGaAs) material system.

The light sources 19 can be viewed as the input layer of the network 11 in the photonic network 11 . A highly reflective mirror coating 31 can be applied to the left outside of the monolithic network 11 , which forms a respective resonator mirror of the laser light sources 19 . A transition between a laser light source 19 and a waveguide 13 can have a less strongly reflecting mirror coating (not shown). This forms a further resonator mirror of a respective laser light source 19. A decoupling of light from the laser resonator and a coupling of the light into the waveguide 13 is thus made possible.

A light source 19 can also be coupled to the respective optical input 15 of the associated waveguide 13 in such a way that light-generating and light-conducting layers of the light source 19 lie in the same plane as light-conducting layers of the waveguide 13 (not shown). As a result, the light from the light source 19 is coupled directly into the associated waveguide 13 .

The waveguides 13 are in the form of quantum well waveguides and have one or more quantum wells which are structured in such a way that a light-guiding effect is established. The quantum wells have a band gap that is larger than a band gap for generating photons in the light sources. This can be achieved by quantum well mixing. This is also known as Quantum Well Intermixing per se.

In the material system, the waveguides 13 also have a slightly higher optical refractive index than regions of the material system adjoining the waveguides 13 . This allows the waveguides 13 to guide light based on the effect of total internal reflection. The difference between the optical refractive indices of a waveguide 13 and an adjacent area can be in the hundredth or thousandth range.

In a material system based on InAlGaAs, the refractive index is about 3.5. In contrast, the waveguides 13 can have a refractive index of 3.501. Thus, a critical angle of total reflection results from arcsin(3.5/3.501) = 88.6°. For example, this allows the use of bends in the waveguides 13 with a radius of 6 µm.

A slight increase in the refractive index in the waveguides 13 can be achieved in that the material forming the waveguides 13 is stressed in compression or tension during the manufacture of the monolithic network 11 . This is also known in and of itself.

The control element 23 allows the optical refractive index of the microring resonator 21 to be adjusted. The microring resonator 21 can therefore be brought into resonance with the adjacent waveguides 13 by means of the control element 23 in order to achieve effective coupling between these waveguides 13 .

The importance of a waveguide 13 in the photonic network 11 can be adjusted by means of a weighting element 25 . A respective waveguide 11 has no mixed quantum wells in the area of a weighting element 25, so that the band gap in the area of a weighting element 25 corresponds to the energy of the photons provided by the light source 19.

A respective weighting element 25 can be adjusted between two states, for example by means of an electrical signal. In a first state of the weighting element 25, incoming photons can be absorbed. In a second state, population inversion can be achieved and the weighting element 25 is thus transparent to incoming photons. In intermediate states between the first and second state, incoming photons can be partially absorbed or transmitted, with the transmission increasing the closer the intermediate state is to the second state.

A pulsating element 27 can be regarded as a "spiking neuron" or "firing neutron". In this case, the respective waveguide 13 has no mixed quantum wells in the region of a respective pulsating element 27 . The band gap in the area of a pulsating element 27 can thus correspond to the energy of the photons provided by the light source.

A respective pulsating element 27 can be brought into a state in which population inversion occurs, in particular by means of an electrical control. Incoming light can be amplified in a strongly non-linear manner, so that a non-linear behavior is simulated.

The terminating elements 29 can be viewed as the output layer of a network 11 . The processed information can be read out of the network 11 by means of the terminating elements 29 .

Each termination element 29 can be designed as a detector for incoming light. A respective waveguide 13 has no mixed quantum wells in the area of a termination element 29, so that absorption of the arriving photons is possible. In particular, the semiconductor layers forming the terminating elements 29 are designed as photodiodes and can be subjected to a blocking voltage.

The photonic network 11 can be viewed as an artificial neural network. The photonic network 11 is therefore suitable, for example, for applications in the field of artificial intelligence, such as machine learning.

Reference List

11

network

13

waveguide

15

Entry

17

Exit

19

light source

21

micro ring resonator

23

control

25

weight element

27

pulsating element

29

final element

31

mirroring

Claims (19)

Photonic network with: a large number of optical waveguides (13) running parallel to one another, each waveguide (13) having an optical input (15) and an optical output (17), a large number of optoelectronic light sources (19), in particular laser light sources, preferably laser diodes, each optical input (15) of the waveguide (13) being coupled to a light source (19) for feeding light, in particular light pulses, into the respective waveguide (13). is, wherein the waveguides (13) and the light sources (19) are formed monolithically in the same material system of the photonic network (11). photonic network claim 1 , characterized in that the material system is an indium aluminum gallium arsenide InAlGaAs material system. photonic network claim 1 or 2 , characterized in that in the material system the waveguides (13) are formed at least in sections as quantum well waveguides, each waveguide (13) having at least one or more quantum wells. photonic network claim 3 , characterized in that the one or more quantum wells of the quantum well waveguides have a band gap corresponding to an energy difference which is greater than the energy of the photons emitted by the light sources (19). photonic network claim 3 or 4 , characterized in that the or each quantum well of the quantum well waveguides are manufactured by means of a quantum well mixing process. Photonic network according to one of the preceding claims, characterized in that in the material system the waveguides (13) have a higher optical refractive index than regions of the material system adjoining the waveguides (13). photonic network claim 6 , characterized in that the difference in the optical refractive indices of the waveguide (13) and the adjacent areas is in the hundredth or thousandth range. Photonic network according to one of the preceding claims, characterized in that in the material system the waveguides (13) are at least partially tensioned in compression or tension. Photonic network according to one of the preceding claims, characterized in that at least one microring resonator (21) is formed in the material system between adjacent waveguides (13). photonic network claim 9 , characterized in that the micro ring resonator (21) has a control element (23) for controlling the decoupling of light from a waveguide (13) and for coupling the light into the adjacent waveguide (13). photonic network claim 10 , characterized in that the optical refractive index of the microring resonator (21) can be adjusted by means of the control element (25). Photonic network according to one of the preceding claims, characterized in that at least one and preferably all waveguides (13) have at least one weighting element (25). photonic network claim 12 , characterized in that a respective waveguide (13) in the area of a weighting element (25) has no mixed quantum wells. photonic network claim 12 or 13 , characterized in that a respective weighting element (25) can be brought into a state in which no population inversion occurs. Photonic network according to one of the preceding claims, characterized in that at least one and preferably all waveguides (13) have at least one pulsating element (27). photonic network claim 15 , characterized in that a respective waveguide (13) in the region of a pulsating element (27) has no mixed quantum wells. photonic network claim 15 or 16 , characterized in that a respective pulsating element (27) can be brought into a state in which population inversion occurs. Photonic network according to one of the preceding claims, characterized in that a terminating element (29) is formed at each optical output (17) of the waveguides (13) in the material system. photonic network Claim 18 , characterized in that a respective closing element (29) is designed as a detector for detecting the light arriving at the respective optical output (17).

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