# US 2019/0318233 A1 · Optical synapse

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- Number: US 2019/0318233 A1
- Document ID: US20190318233A1
- Status: Published application
- Kind: A1
- Application number: 15/953,436
- Filed: 2018-04-14
- Published: 2019-10-17
- Earliest claimed: 2018-04-14
- Assignees: International Business Machines Corporation
- Applicants: International Business Machines Corporation
- Inventors: Stefan Abel; Veeresh V. Deshpande; Jean Fompeyrine
- Web page: https://patentgrep.com/patent/US20190318233A1

## CPC

- G06N 3/067: using optical means
- G06N 3/0675: {using electro-optical, acousto-optical or opto-electronic means}
- G02F 1/3501: {Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals}
- G02F 1/355: characterised by the materials used
- H04B 10/40: Transceivers
- H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)}
- G02F 1/3503: {Structural association of optical elements, e.g. lenses, with the non-linear optical device}
- G02F 2203/48: Variable attenuator
- G02F 2203/50: Phase-only modulation
- G06E 3/008: {Matrix or vector computation}
- G06N: COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- G06E: OPTICAL COMPUTING DEVICES (digital storage using optical elements G11C13/04)

## Abstract

An integrated optical circuit for an optical neural network is provided. The integrated optical circuit is configured to process a phase-encoded optical input signal and to provide a phase-encoded output signal depending on the phase-encoded optical input signal. The phase-encoded output signal emulates a synapse functionality with respect to the phase-encoded optical input signal. A related method and a related design structure are further provided.

## Claims

### Claim 1

An integrated optical circuit for an optical neural network, the optical circuit being configured:
to process a phase-encoded optical input signal; and
to provide a phase-encoded optical output signal depending on the phase-encoded optical input signal, the phase-encoded optical output signal emulating a synapse functionality with respect to the phase-encoded optical input signal.

### Claim 2 (depends on 1)

The integrated optical circuit according to claim 1, wherein the integrated optical circuit is configured:
to convert the phase-encoded optical input signal into an amplitude-encoded signal;
to perform a weighting of the amplitude-encoded signal; and
to convert the weighted amplitude-encoded signal into the phase-encoded optical output signal.

### Claim 3 (depends on 1)

The integrated optical circuit according to claim 1, further comprising:
a reference waveguide configured to carry an optical reference signal;
an input waveguide configured to receive the phase-encoded optical input signal, wherein a phase difference between the optical reference signal and the optical input signal represents the phase of the phase encoded optical input signal;
an output waveguide;
an optical interferometer configured to convert the optical reference signal and the optical input signal into an interference signal by superimposition;
a tunable attenuator configured to perform a weighting of the interference signal into a weighted interference signal; and
a phase-shifting device configured to convert the weighted interference signal into the phase-encoded optical output signal by inducing a phase shift in the optical reference signal in dependence on the weighted interference signal.

### Claim 4 (depends on 3)

The integrated optical circuit according to claim 3, wherein the phase-encoded optical output signal comprises a phase shift within a predefined range relative to the optical reference signal.

### Claim 5 (depends on 4)

The integrated optical circuit according to claim 4, wherein the predefined range is a range between 0° and 180°.

### Claim 6 (depends on 1)

The integrated optical circuit according to claim 1, wherein the optical circuit is configured to perform a variable phase shift as a function of a weighting factor of the synapse.

### Claim 7 (depends on 1)

The integrated optical circuit according to claim 1, comprising a power normalization unit configured to perform a normalization of the output power of the phase-encoded optical output signal.

### Claim 8 (depends on 7)

The integrated optical circuit according to claim 7, wherein the power normalization unit comprises an amplifier and a saturated absorber.

### Claim 9 (depends on 3)

The integrated optical circuit according to claim 3, wherein the tunable attenuator is implemented as a tunable absorber.

### Claim 10 (depends on 3)

The integrated optical circuit according to claim 3, wherein the optical interferometer comprises a single-mode interferometer or a multi-mode interferometer.

### Claim 11 (depends on 3)

The integrated optical circuit according to claim 3, wherein the phase-shifting device comprises a non-linear optical material with a non-linear power-to-refractive-index conversion.

### Claim 12 (depends on 11)

The integrated optical circuit according to claim 11, wherein the nonlinear material is selected from the group consisting of: BaTiO3, LiNbO3, ferroelectric perovskites, polymers with non-linear optical properties, chalcogenides and III-V compound semiconductors.

### Claim 13 (depends on 3)

The integrated optical circuit according to claim 3, wherein the phase-shifting device comprises a phase change material.

### Claim 14 (depends on 13)

The integrated optical circuit according to claim 13, wherein the phase change material is selected from the group consisting of: V4O7, V6O11, V2O3, V6O13, V5O9, VO, V8O15, NbO2, Ti2O3, LaCoO3, Ti3O5, SmNiO3, NdNiO3, PrNiO3 Fe3O4, and chalcogenides.

### Claim 15 (depends on 3)

The integrated optical circuit according to claim 3, wherein the phase-shifting device is a plasma dispersion modulator.

### Claim 16 (depends on 3)

The integrated optical circuit according to claim 3, wherein the phase-shifting device comprises:
an optical cavity comprising a non-linear material; and
a gate waveguide coupled to the optical cavity and configured to guide the weighted interference signal to the optical cavity and to change the refractive index of the non-linear material in dependence on the optical power of the weighted interference signal;
wherein the optical cavity is configured:
to receive the optical reference signal;
to induce a phase shift in the optical reference signal; and
to provide the phase-encoded optical output signal.

### Claim 17

A method for emulating a synapse functionality, the method comprising:
providing an integrated optical circuit;
processing, by the integrated optical circuit, a phase-encoded optical input signal;
emulating, by the integrated optical circuit, a synapse functionality with respect to the phase-encoded optical input signal; and
providing, by the integrated optical circuit, a phase-encoded optical output signal.

### Claim 18 (depends on 17)

The method according to claim 17, the method comprising:
converting the phase-encoded optical input signal into an amplitude-encoded signal;
performing a weighting of the amplitude-encoded signal; and
converting the weighted amplitude-encoded signal into the phase-encoded optical output signal.

### Claim 19 (depends on 17)

The method according to claim 17, the method comprising:
carrying, by a reference waveguide, an optical reference signal;
receiving, by an input waveguide, the phase-encoded optical input signal, wherein a phase difference between the optical reference signal and the optical input signal represents the phase of the phase encoded input signal;
converting, by an optical interferometer, the optical reference signal and the optical input signal into an interference signal by superimposition;
weighting, by a tunable attenuator, the interference signal, thereby converting it into a weighted interference signal; and
converting, by a phase-shifting device, the weighted interference signal into the phase-encoded optical output signal by inducing a phase shift in the optical reference signal in dependence on the weighted interference signal.

### Claim 20

A design structure tangibly embodied in a machine readable medium for designing, manufacturing or testing an integrated circuit, the design structure comprising:
an optical circuit configured:
to process a phase-encoded optical input signal; and
to provide a phase-encoded optical output signal, the phase-encoded output signal emulating a synapse functionality with respect to the phase-encoded optical input signal.

### Claim 21 (depends on 20)

The design structure according to claim 20, the design structure comprising:
a reference waveguide configured to carry an optical reference signal;
an input waveguide configured to receive the phase-encoded optical input signal, wherein a phase difference between the optical reference signal and the optical input signal represents the phase of the phase-encoded optical input signal;
an output waveguide;
an optical interferometer configured to convert the optical reference signal and the optical input signal into an interference signal by superimposition;
a tunable attenuator configured to perform a weighting of the interference signal into a weighted interference signal; and
a phase-shifting device configured to convert the weighted interference signal into the phase-encoded optical output signal by inducing a phase shift in the optical reference signal as a function of the weighted interference signal.

### Claim 22

An optical neural network, comprising:
a plurality of integrated optical circuits as synapses, each of at least a subset of the integrated optical circuits being configured:
to process a phase-encoded optical input signal; and
to provide a phase-encoded optical output signal depending on the phase-encoded optical input signal, the phase-encoded optical output signal emulating a synapse functionality with respect to the phase-encoded optical input signal.

### Claim 23 (depends on 22)

The optical neural network according to claim 22, comprising a plurality of further integrated optical circuits as neuron circuits, each of at least a subset of the neuron circuits being configured:
to process a plurality of phase-encoded optical input signals; and
to provide a phase-encoded optical output signal, the phase-encoded optical output signal emulating a neuron functionality with respect to the plurality of phase-encoded optical input signals.

### Claim 24 (depends on 23)

The optical neural network according to claim 23, each of at least a subset of the neuron circuits being configured:
to convert the plurality of phase-encoded optical input signals into a plurality of amplitude-encoded signals;
to combine the plurality of amplitude-encoded signals into a summation signal; and
to perform a non-linear conversion of the summation signal into the phase-encoded optical output signal.

### Claim 25 (depends on 23)

The optical neural network according to claim 23, each of at least a subset of the neuron circuits comprising:
a reference waveguide configured to carry an optical reference signal;
a plurality of input waveguides configured to receive the plurality of phase-encoded optical input signals, wherein phase differences between the optical reference signal and the optical input signals represent the respective phase of the respective phase encoded input signal;
an output waveguide;
an optical interferometer system configured:
to superimpose the plurality of optical input signals and the optical reference signal into a plurality of first interference signals;
to superimpose the plurality of first interference signals into a second interference signal; and
a phase-shifting device configured to provide the phase-encoded optical output signal as a function of the second interference signal.