Random number generator

1. A random number generation system, comprising:

a light source configured to generate light pulses;

a driving unit configured to drive said light source by applying a time varying signal comprising a series of pulses to the light source, wherein when applied to the light source each pulse in the time varying signal generates a light pulse, the frequency of the pulses being less than or equal to 4.0 GHz such that the phase of each light pulse has a random relationship to the phase of each subsequently generated light pulse, and such that each light pulse is generated with at least two local maxima in the temporal intensity profile, wherein each light pulse is generated with a spike-like temporal intensity profile followed by a plateau-like temporal intensity profile, wherein a first local maxima is associated with the part of the light pulse with a spike-like temporal profile and a second local maxima is associated with the part of the light pulse with a plateau-like temporal intensity profile;

an interference module, configured to interfere input light pulses, wherein the generated light pulses having at least two local maxima in the temporal intensity profile are inputted to the interference module, said interference module configured to transform the random phase of said input light pulses into a random amplitude of an output light pulse by interference of the input light pulses; and

an optical electrical signal converter and an analogue to digital converter configured to generate a sequence of N-bit random integers from the random amplitudes of a sequence of output light pulses.

2. The random number generation system of claim 1 , wherein the intensity of the part of the light pulse with a plateau-like temporal intensity profile does not vary by more than 20%.

3. The random number generation system of claim 1 , wherein the part of the light pulse with a plateau-like temporal intensity profile has a longer duration than the part of the light pulse with a spike-like temporal intensity profile.

4. The random number generation system of claim 1 , wherein the part of the light pulse with a plateau-like temporal intensity profile has a sharper wavelength distribution than the part of the light pulse with a spike-like temporal intensity profile.

5. The random number generation system of claim 1 , wherein said light source is a laser and said driving unit applies a time varying driving signal to said laser.

6. The random number generation system of claim 5 , wherein the driving signal is a time varying voltage or current and the amplitude of the maximum voltage or current is at least 25% greater than the voltage or current required to reach the lasing threshold when operating under a DC voltage or current only.

7. The random number generation system of claim 5 , wherein the driving signal pulses have a substantially flat-topped profile.

8. The random number generation system of claim 1 , wherein said interference module comprises:

a fibre optical ring resonator.

9. The random number generation system of claim 1 , wherein the optical electrical signal converter is a photodiode.

10. The random number generation system of claim 1 , further comprising a finite impulse response filter configured to reduce bias and/or correlations in the output of the analogue to digital converter.

11. The light source unit of claim 10 , wherein the output of said finite impulse response filter is

y

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c

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x

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where x[n] is the nth output of the analogue to digital converter, M ≥1 and is an integer selected by the user and gives the number of input samples, k ≥1 and is an integer selected by the user and gives the number of bits of the output y[n], and the c i values are real constants selected by the user.

12. The random number generation system of claim 1 , wherein the light source is a semiconductor laser diode that is pulse driven.

13. The random number generation system of claim 1 , wherein said interference module comprises:

an asymmetrical Mach-Zehnder interferometer.

14. The random number generation system of claim 13 , wherein an optical path length difference between a first arm and a second arm of the asymmetrical Mach-Zehnder interferometer corresponds to an integer multiple of the time between emission of the light pulses to within a tolerance of 20% of the time between emission of the light pulses.

15. A method of random number generation, comprising:

applying a time varying driving signal comprising a series of pulses to a light source, wherein when applied to the light source each pulse in the time varying signal generates a light pulse, the frequency of the pulses being less than or equal to 4.0 GHz such that the phase of each light pulse has a random relationship to the phase of each subsequently generated light pulse and such that each light pulse is generated with at least two local maxima in the temporal intensity profile, wherein each light pulse is generated with a spike-like temporal intensity profile followed by a plateau-like temporal intensity profile, wherein a first local maxima is associated with the part of the light pulse with a spike-like temporal profile and a second local maxima is associated with the part of the light pulse with a plateau-like temporal intensity profile;

inputting the light pulses into an interference module;

interfering said light pulses having at least two local maxima in the temporal intensity profile at the interference module, such that the random phase of said light pulses is transformed into a random amplitude of an output light pulse; and

generating a sequence of N-bit random integers from the random amplitudes of a sequence of output light pulses.