EP2359236A2

EP2359236A2 - Quantum random number generator based on diffraction of high-order grating

Info

Publication number: EP2359236A2
Application number: EP09829365A
Authority: EP
Inventors: Witjaksono Gunawan
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2008-11-03
Filing date: 2009-11-03
Publication date: 2011-08-24
Also published as: MY146870A; WO2010062161A3; EP2359236A4; WO2010062161A2

Abstract

A method and apparatus (10) for generating random numbers using high-order grating (12) by wave diffraction of emitting photons from the grating (12) is disclosed. The apparatus (10) includes a particle source (11) capable of emitting a source of particles, a high-order grating (12) including output surfaces (22, 23), said high-order grating being disposed in relation to said particle source so that said source of particles encounter said high-order grating (12) for diffraction and particle which goes through constructive interference emits through either output surfaces (22, 23) of said grating (12), and at least one detector for capturing said emitted particle to a random signal to be processed for outputting a random number.

Description

Quantum Random Number Generator based on Diffraction of High- Order Grating

Field of Invention

The present invention relates generally to a random number generator and more particularly to a quantum random number generator based on diffractions of high-order grating.

Background of the Invention

Pseudo-random numbers are sequence of numbers produced by a deterministic algorithm where conventional software-based random number generators (RNGs) produce pseudo-random numbers. The periodic sequence of number is completely determined. In information security application, such as quantum key distribution (QKD) , this system will be unsecured if an eavesdropper could predict, and even worse that the cryptography potential on such system would be zero if the eavesdropper could calculate the random number exactly. True- random numbers are sequence of numbers relying upon randomness in physical or natural events. Thermal noise in electronics and radioactive decay are believed to provide truly random events .

There are a few ways and attempts that have been made to produce hardware random numbers generators. Below is shown some prior art documents which explain such methods or attempts .

First prior arts, US Patent No. 6,745,217, by Figotin

Aleksandr, Vitebskiy Ilya, Popovich Vadim, Stetsenko

Gennady, Molchanov, Stanislav, Gordon Alexander. Quinn

Joseph, Stavrakas Nicholas, issued Jun 1, 2004, is using radioactive decay as a source of randomness, or the use of thermodynamic processes such as diode current fluctuations or Johnson noise measured on the voltage across a resistor

(see, for example, US Patent No. 6,571,263, by Nagai

Gouichiro, issued on May 27, 2003) .

Other prior art teaches random generation method uses outputs of a beam splitter to establish random numbers from the path of photon (US Patent No. 6,609,139 by Dultz Wolfgang, Dultz Gisela, Hildebrandt Eric, Schmitzer Heidrun, which is issued on August 19, 2003) . A commercial implementation is sold by id Quantique S. A. of Carouge, Switzerland. A light source emits photons which pass through a beam splitter. Whenever a photon is emitted, it takes one the two possible paths (with a small probability to get reflected or absorbed) . If it ends up in the single photo- detector Dl then it generates binary value "1", whereas if it ends up in single photo-detector D2 it generates binary value "0". Fig. 1 shows such system, which consists of photon transmitter (attenuated laser, or LED) , passive optical components (attenuator, half-wave plate, polarizes, and beam splitter), and receiver (lenses and photo- detectors) .

These implementations of true random number generators suffer some drawbacks. The first two prior arts either have a safety-concern issue or complicated system circuitry, which are not suitable for commercial applications. The third prior art uses a bulk optical component (beam-splitter) and thus giving a considerably big size of the whole systems. Furthermore, in this prior art requires additional passive optical components with the photon source in order to produce a single photon coming into the beam-splitter. These requirements further increase the size of the quantum random number generator.

Other prior art document is US Patent Application No. US 2006/0010182 Al, by Altepeter Joseph B, Jeffrey Evan, and

Kwiat Paul G, publication date is Jan 12, 2006, describes wherein undeterministic random number generator utilizes a single photo-detector, which detects a photon at a particular time segment as shown in Fig. 2. Events characteristics of a random process are registered, and a particular time segment, from among a set of time segments, is identified based upon registration of an event within the time segment, and a value is associated based on the identified time segment. The event is a detection of a particle by a particle detector such as a photon detector. A random number is outputted based at least upon the associated value. Outputting of the random numbers may be followed by a whitening process. The source of particle may be driven to provide various specified probability distributions of values.

The disadvantage of such implementation is that a complex circuit is needed in order to account for the synchronization between the laser signal, photodetector action, and data processing of received signal to determine the random outputs (Time Interval Analyzer) . This prior art is very sensitivity to the environment, which makes the random number output is biased. Fig. 2 shows component configuration to produce quantum random numbers, for that such a system, based on time interval.

Many true random number generators have been reported up to now, i.e. noise-based randomness, beam-splitter and time- based randomness, but none of those inventions tackle the issue of miniaturization or even integration. The present invention has overcome the drawbacks of the existing apparatus and methods by providing a preferred quantum random number generator, which is disclosed in the present invention, reveals undeterministic random number generator that later can be integrated with all active and passive optical components. This invention is based on the quantum mechanics of the photon source which is diffracted by the second-order grating and detected by multi single-photon detectors producing random numbers.

An objective of the present invention is to provide a random number generator based on diffractions of high-order grating which is able to increase randomness probability.

Another objective of the present invention is to provide a random number generator which can be integrated with all active and passive photonic devices, thus, make further miniaturization of such system is possible.

These and other advantages will become apparent to those skilled in this art upon reading the following detailed description in conjunction with the accompanying drawings.

Summary of the Invention

The preferred embodiment of the disclosed invention to generate random number is based on the diffraction of particle, such as photon, of high-order grating. Events of producing of a random process are captured by means of signal detection of low light detector from diffracted photon after passing through second-order grating. Signal detection of a single photon may come from zeroth-order, first-order or second-order of diffracted wave, in which the photon is originated from coherent or incoherent light source, i.e. laser or light emitting diode (LED) .

In accordance to the invention, the particle that propagates within the high-order grating experiences reflection, transmission and diffraction, resulting in wave interferencing and only the photon that goes through constructive interference escapes through the surface and detected by low light detector. The detector signals or their counting events represent value of random events, or random sequence .

The generation of photon based on diffraction wave creates completely uncertain path which of the outputs photon will take. With possibility of multi diffraction-order from the high-order grating, this increases randomness probability. Significant advantage of using high-order grating for quantum random number generator is possible integration of active photonic devices, i.e. LED and Laser, and passive photonics devices, i.e. grating and attenuator, thus, make further miniaturization of the such system is possible. Brief Description of the Drawings

Other objects, features, and advantages of the invention will be apparent from the following description when read with reference to the accompanying drawings. In the drawings, wherein like reference numerals denote corresponding parts throughout the several views:

Fig. 1 shows a diagram of a prior art random number generator which uses beam splitter method for generating random binary digits;

Fig. 2 depicts a diagram of another prior art random number generator based on time interval; and

Fig. 3 illustrates a schematic diagram of the random number generator of the present invention based on diffraction of high-order grating.

Detailed Description of the Preferred Embodiments

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures and/or components have not been described in detail so as not to obscure the invention. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

A preferred method of practicing the present invention is now described with reference to Fig. 3 wherein a Quantum Random Number Generator, designated by numeral 10, is depicted schematically. The quantum random number generator (10) includes a light source (11) , such a semiconductor laser to produce photon source, for example, is directed along path (13) onto a grating (12) for generating random numbers by wave diffraction of emitting photons from the grating (12) . The grating (12) used in the present invention is a high-order grating which is preferably a second-order grating. The random emitting photons from the grating (12) is then captured by a detector system (14), such as a photodetector, to a random signal. The detected signal is then processed by an electronic circuit (not shown) and a digital circuit (not shown) for outputting a random number.

The light source (11) of the semiconductor laser emits light either along its longitudinal cavity for edge-emitting light source or its transverse cavity for surface-emitting light source, that produces continuous wave or optical pulse (shown, by way of example) , as driven by an electrical or optical module. Other light sources, such as light emitting diode

(LED) , are also encompassed within the scope of the present invention. However, the light source (11) may be referred to herein as a laser, without limitation. The produced light is generated by either spontaneous or stimulated emission from the laser light source (11) .

The laser (11) is provided with a metal contact (15) on top (Ha) of the laser (11) and at the bottom (lib) of the laser

(lib) for exciting the laser (11) by electrical pumping to produce the photon light source. The laser (11) could be excited by optical pumping directly to the laser (11) . The generation of the light within the laser (11) occurred in an active region (16) of the laser cavity (25) . A high-reflection layer (17) is deposited at a first end side of the laser (11) to prevent the generated light exits through this first end side as shown in Fig. 3.

The grating (12) is positioned in front of the laser (11), adjacent a second side (18) of the laser (11) which is opposing the first side surface of the laser (11) where the high-reflection layer (17) is deposited. The generated light which exits through the second side (18) of the laser (11) via the path (13) will then hit and propagate within the grating (12) and the emitted photons are diffracted by the grating (12). The grating (12) is positioned in such a way to make optimum coupling between the incoming light from the laser

(11) and the feedback actions by the grating (12) . The grating position could be higher, parallel, or lower compared to the position of the active region (16) of the laser (11) . The optical path or direction of the emitted photon defines the order of diffraction.

On standard grating, which is using first-order grating, the optical path is forward wave and backward wave, when the angle of incident (θj_.) is less than the critical angle for maintaining total internal reflection. Hence, the first-order grating produces zeroth-order diffraction for the feed-forward wave and first-order for the feedback wave.

With the second-order grating (12) used in the present invention, the diffraction of the particle, i.e. the photon, has three different directions which are the zeroth-order diffraction for forward wave, first-order diffraction for radiating wave at angle of 90° both to the surface and second- order diffraction for feedback wave. The shape of the grating

(12) could be rectangular, sinusoidal, triangular, combination of patterns, as well as chirped pattern. The grating (12) can be made from semiconductor material or other material, with a grating duty cycle corresponding to both a wavelength range of the emitting laser (11) and the spectrum range of the photodetector (14) in order to have maximum light reception.

In accordance to the present invention, the second-order grating (12) is a periodic variation of refractive index. The variation of the refractive index is formed by alternating the deposited material. The period of the grating is determined by the operating wavelength. Additionally the operating wavelength is also affected by the refractive index of the grating (12) .

The grating (12) includes an absorbing layer (19) that suppresses excessive photon energy from the light source (11) and thus resulting the diffracted light from the grating (12) only consists of small number of photon or possible a single photon. The absorbing layer (19) could have the same material and composition as the active region (16) of the laser (11) and thus simplified the preparation of active region (16) and absorbing layer (19) in the grating (12) . With the inclusion of the absorbing layer (19) to the present invention, the light source (11) can be operated in any operating conditions, such as below threshold condition which is operating in spontaneous emission as LED or above threshold condition which is operating in stimulated emission as a laser. With the present absorbing layer (19) incorporated with the grating (12), some of the light produced by the laser (11) is absorbed by this layer, hence, the absorbing layer (19) acts as an attenuator. Therefore, the present invention eliminates the need of bulk optics such as attenuator filter in the system thus reducing the overall dimension of the system and making it possible for an integration of photonic devices of true random number generator.

Another high-reflection layer (20) is deposited at a first end side of the grating (12) to prevent the light exits through this first end side. The opposing end side of the grating (12) which is a second end side (21) adjacent the second side (18) of the laser (11) is slanted to prevent the light coming from the grating (12) back to the light source (11) . As the wave moves forward and back in the longitudinal cavity of the grating region, there is possibility that the feedback light escapes from the second end side (21) of the grating (12) and degrade the light source operation. With this slanted interface at the second end side (21), the feedback wave is being reflected to other directions, hence, the directivity of the photon can be controlled.

The top (22) and bottom (23) of the grating (12), where the light is emitted (26, 27), is covered with an anti-reflection layer (24) respectively in order to optimize the emitting light and to reduce back-reflection to the grating cavity. A first photodetector (14a) is placed on the face at the top

(22) of the grating (12) and a second photodetector (14b) is placed on the face at the bottom (23) of the grating (12) to capture the respective emitted light (26, 27) . However, it is completely uncertain which of the outputs photon (26, 27) will take. The emitted light (26, 27) is the random emitting photon. This elementary process is utilized according to the invention to generate the random sequence. The photodetectors (14) used are preferable single-photon detectors.

Single-photon denotes the sensitivity of the detector (14) to single photons of a wavelength emitted by the light source (11). Detector (14) may be an avalanche photodiode, for example, or a photomultiplier tube. When detector registers a photon, it generates an output pulse, which is fed to the electronic circuit and processed by the digital circuit which is also part of a data processing module to product random numbers. The present invention can be fabricated with the standard semiconductor processing and applicable in all areas in which true random numbers need to be generated, particularly in the field of information security, telecommunication, statistical research and gaming.

As will be readily apparent to those skilled in the art, the present invention may easily be produced in other specific forms without departing from its essential characteristics. The present embodiments is, therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within therefore intended to be embraced therein.

Claims

1. A method for generating random numbers, the method comprising the steps of: emitting a source of particles along a path (13); diffracting said source of particles from said path (13) which propagates within a high-order grating (12) so as to bring said particles into interference; directing the particle which goes through constructive interference to emit through either surfaces of said grating

(12); and capturing said emitted particle with respective detection device to a random signal to be processed for outputting a random number.

2. The method for generating random numbers as claimed in claim 1, wherein said method further comprising the step of providing an absorbing layer (19) which suppresses excessive particle energy from the source of particles.

3. The method for generating random numbers as claimed in claim 1, wherein said high-order grating (12) is a second- order grating.

4. The method for generating random numbers as claimed in claim 1, wherein said source of particles are diffracted to three directions which are zeroth-order diffraction for forward wave, first-order diffraction for radiating wave at angle of 90° and second-order diffraction for feedback wave.

5. The method for generating random numbers as claimed in claim 1, wherein said step of directing the particle includes depositing a high-reflection layer (20) at a first end side of said grating (12) to prevent said source of particles exit through said first side, and providing at a second end side (21) of said grating (12) which opposing to said first end side, with slanted surface to prevent the diffracted particle back to the particle source.

6. An apparatus (10) for generating random numbers, the apparatus (10) comprising: a particle source (11) capable of emitting a source of particles along a path (13); a high-order grating (12) including output surfaces (22, 23), said high-order grating being disposed in relation to said particle source so that said source of particles encounter said high-order grating (12) for diffraction and particle which goes through constructive interference emits through either output surfaces (22, 23) of said grating (12); and at least one detector for capturing said emitted particle to a random signal to be processed for outputting a random number.

7. The apparatus (10) for generating random numbers as claimed in claim 6, wherein said particle source (11) is semiconductor laser which produces coherent light source.

8. The apparatus (10) for generating random numbers as claimed in claim 6, wherein said particle source (11) is a light emitting diode which produces incoherent light source.

9. The apparatus (10) for generating random numbers as claimed in claim 7, wherein said laser (11) emits light along its longitudinal cavity for edge-emitting light source.

10. The apparatus (10) for generating random numbers as claimed in claim 7, wherein said laser (11) emits light along its transverse cavity for surface-emitting light source.

11. The apparatus (10) for generating random numbers as claimed in claim 7, wherein said laser (11) includes a metal contact on top and at the bottom of said laser (11) for exciting said laser (11) by electrical pumping to produce light source.

12. The apparatus (10) for generating random numbers as claimed in claim 11, wherein said light source is generated in an active region (16) of the laser (11) .

13. The apparatus (10) for generating random numbers as claimed in claim 11, wherein said laser (11) further comprising a high-reflection layer (17) deposited at a first end side of said laser (11) to prevent said generated light exits through the first end side.

14. The apparatus (10) for generating random numbers as claimed in claim 6, wherein said high-order grating (12) is positioned in front of said laser (11) adjacent a second end side (18) of said laser (11) which is opposing the first end side of said laser (11) .

15. The apparatus (10) for generating random numbers as claimed in claim 6, wherein said high-order grating (12) is a second-order grating.

16. The apparatus (10) for generating random numbers as claimed in claim 15, wherein said grating (12) includes an absorbing layer (19) which suppresses excessive particle energy from the source of particles and said absorbing layer (19) could have same material and composition as the active region (16) of said laser (11) .

17. The apparatus (10) for generating random numbers as claimed in claim 15, wherein said grating (12) is deposited with a high-reflection layer (20) at a first end side of said grating (12) and provided with a slanted surface at a second end side (21) of said grating which is adjacent to said second end side (18) of said laser (11).

18. The apparatus (10) for generating random numbers as claimed in claim 6, wherein said high-order grating (12) having output surfaces (22, 23) associated with two detectors (14a, 14b) where each output associated with a detector respectively for detecting single photon.

19. The apparatus (10) for generating random numbers as claimed in claim 18, wherein said detectors are photodetectors such as single-photon detectors.

20. The apparatus (10) for generating random numbers as claimed in claim 18, wherein each of said output surfaces (22, 23) is covered with an anti-reflection layer (24) to optimize the emitting light and to reduce back-reflection to the grating (12) .