Optical synapse

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, 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.

2. 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.

3. The integrated optical circuit according to claim 1 , wherein the phase-encoded optical output signal comprises a phase shift within a predefined range relative to the optical reference signal.

4. The integrated optical circuit according to claim 3 , wherein the predefined range is a range between 0° and 180°.

5. 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.

6. 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.

7. The integrated optical circuit according to claim 6 , wherein the power normalization unit comprises an amplifier and a saturated absorber.

8. The integrated optical circuit according to claim 1 , wherein the tunable attenuator is implemented as a tunable absorber.

9. The integrated optical circuit according to claim 1 , wherein the optical interferometer comprises a single-mode interferometer or a multi-mode interferometer.

10. The integrated optical circuit according to claim 1 , wherein the phase-shifting device comprises a non-linear optical material with a non-linear power-to-refractive-index conversion.

11. The integrated optical circuit according to claim 10 , 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.

12. The integrated optical circuit according to claim 1 , wherein the phase-shifting device comprises a phase change material.

13. The integrated optical circuit according to claim 12 , wherein the phase change material is selected from the group consisting of: VO2, V4O7, V6O11, V2O3, V6O13, V5O9, VO, V8O15, NbO2, Ti2O3, LaCoO3, Ti3O5, SmNiO3, NdNiO3, PrNiO3, Fe3O4 and chalcogenides.

14. The integrated optical circuit according to claim 1 , wherein the phase-shifting device is a plasma dispersion modulator.

15. The integrated optical circuit according to claim 1 , 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.

16. 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, the method further 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.

17. The method according to claim 16 , 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.

18. 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, wherein the optical circuit uses a phase to encode information in an optical domain, 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.

19. 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,

wherein the integrated optical circuit uses a phase to encode information in an optical domain,

further 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, 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.

20. The optical neural network according to claim 19 , 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.