Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F7/00—Methods or arrangements for processing data by operating upon the order or content of the data handled
  • G06F7/58—Random or pseudo-random number generators
  • G06F7/588—Random number generators, i.e. based on natural stochastic processes
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
  • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
  • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
  • H01S3/1106—Mode locking
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/06226—Modulation at ultra-high frequencies
  • H01S5/0623—Modulation at ultra-high frequencies using the beating between two closely spaced optical frequencies, i.e. heterodyne mixing
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
  • H01S5/0657—Mode locking, i.e. generation of pulses at a frequency corresponding to a roundtrip in the cavity
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/3013—AIIIBV compounds
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F2207/00—Indexing scheme relating to methods or arrangements for processing data by operating upon the order or content of the data handled
  • G06F2207/58—Indexing scheme relating to groups G06F7/58 - G06F7/588
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/06209—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in single-section lasers
  • H01S5/06213—Amplitude modulation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
  • H01S5/0651—Mode control
  • H01S5/0652—Coherence lowering or collapse, e.g. multimode emission by additional input or modulation
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
  • H04L9/0861—Generation of secret information including derivation or calculation of cryptographic keys or passwords
  • H04L9/0869—Generation of secret information including derivation or calculation of cryptographic keys or passwords involving random numbers or seeds

Definitions

• the present invention relates to random number generators (RNGs), in particular to generators based on the intrinsic randomness of quantum observables in multimode laser cavities with variable gain or loss.
• RNGs random number generators
• Random numbers form sequences of numbers or symbols that lack any pattern, appear random.
• a random number generator is a computational or physical device designed to generate random numbers. RNGs can be classified in pseudo-RNGs (PRNGs), computational algorithms, and true-RNGs (TRNGs).
• PRNGs pseudo-RNGs
• TRNGs true-RNGs
• TRNGs are physical devices and can be subdivided into classical RNGs (CRNGs) based on classical deterministic laws, and quantum RNGs (QRNGs) based on quantum effects.
• CRNGs classical RNGs
• QRNGs quantum RNGs
• the patent application "ultrafast quantum random number generator and system thereof" by Pruneri et al [5] discloses a QRNG based on measuring quantum phase diffusion in a pulsed single-mode semiconductor laser. By modulating the laser from below to above threshold, optical pulses with nearly identical intensities and completely randomized phases are generated. Then, by using an external interferometer, the random phases are translated into random amplitudes, which can be digitised with a PIN detector. Instead of one laser source and an interferometer, two laser sources can be used together with a combiner. The technique allows for ultrafast operation regimes, and recent publications have shown bitrates up to 40-80 Gbps [7,8].
• the invention is based on the transformation of the random phases of the modes of a multimode laser into random intensity patterns that can be detected with a fast photodiode.
• the invention comprises the steps of utilizing a multimode laser whose net gain per round trip is modulated continuously from positive to negative values and viceversa by means of an electrical pulse driver, maintaining net gain per round trip positive for a longer period than the round trip time of the cavity, maintaining net gain per round trip negative for a longer period than the round trip time of the cavity and detecting the resulting beating pattern between the longitudinal modes of the laser cavity utilizing a fast photodiode (PIN).
• PIN fast photodiode
• a multimode laser for implementing the invention, for example a Fabry Perot cavity semiconductor laser whose multimode response is achieved through proper wavelength selective reflectors or a fiber ring laser comprising fiber Bragg gratings for mode selection and a semiconductor optical amplifier as gain medium.
• Any laser cavity which has at least two modes is in principle suitable as long as the net gain, i.e. the difference between gain and loss in the cavity, of at least one of the at least two modes can be properly modulated, in particular to achieve sufficiently negative net gain values and, correspondingly, large phase diffusion.
• the laser gain, the loss of the cavity or, alternatively, both the laser gain and cavity loss can be modulated.
• the laser experiences two stable working regimes: (i) above threshold, in which the different longitudinal modes of the multimode laser will create a random intensity pattern characterized by the frequency spacing and the relative phases between the modes, and (ii) below threshold, in which the laser cavity field is forced to operate in a spontaneous emission regime, resetting and randomising in this way the relative phases between the modes for the next modulation period.
• Fig. 2 shows another set up.
• Fig. 3 shows the autocorrelation function for two operating regimes of a multi-mode laser.
• Fig 1 shows a first set up for putting into practice the invention, in which a two-mode laser is obtained via selective filtering within the cavity of a multimode laser diode (MMLD).
• the MMLD is modulated by means of an electrical pulse driver (PD). Since only two modes are selected in the example, the beating pattern when detected with the photodiode (PIN) shows cosine dependence with a frequency given by the mode spacing (frequency difference between modes rri2 and rri3 in the figure) and initial phase ⁇ , ⁇ given by the phase difference between the modes in that particular period.
• An optical isolator (01) can be added to avoid optical back reflections into the laser cavity.
• the resulting intensity pattern shows cosine dependence, due to the dual- mode emission, with a random initial phase.
• sampling subsequent pulses produces digitization of random amplitudes, since each pulse generated by modulating the effective laser cavity gain is built on the random initial phase of the two modes.
• the larger the number of modes involved in the beating the more complex the resulting intensity pattern and the larger the number of random samples that can be extracted within each net gain modulation period.
• modulating the net gain of the laser cavity is essential for the system to provide quantum random samples (numbers). If the net gain were kept constant above threshold, mode beating would still exist but correlations would be present between the pulses leaving the cavity. If the net gain were modulated with a frequency correlated to the round trip of the cavity, this mode beating could become what is known as mode-locking producing a train of periodic pulses.
• a similar structure for an integrated version of the scheme could be made as follows: placing the active material inside or on top of a photonic integrated circuit (PIC), and using the cleaved facets of the chip itself as mirrors.
• the spectral filtering can be achieved either by placing gratings on both sides of the active material, or by using a ring-like structure.
• Fig. 2 an active material such as InP or InGaAsPis placed in a Fabry Perot cavity with highly reflective end mirrors.
• the spectral reflectivity of the mirrors can be engineered so that the cavity itself acts as a filter allowing only a few modes to oscillate.
• the two reflective mirrors can filter two desired modes (CRCi,2).
• CRCi,2 desired modes
• By electrically pumping the active medium lasing can take place and a broad multimode optical spectrum is generated.
• the separation between the mirrors and the refractive index of the material in between determines the mode spacing.
• the cavity is designed so that the mode spacing is smaller than the detection bandwidth, the inter-mode beating of the laser can be resolved with a fast photodiode (PIN).
• Fig. 2b the active material is deposited on top of a photonic chip and using the reflection produced by the cleaved facets of a chip the cavity is created.
• the spectral filtering is obtained by means of gratings.
• Fig. 3 shows the autocorrelation function for two operating regimes: (upper picture) the laser never reaches the spontaneous emission regime, and (lower picture) the laser successfully reaches the spontaneous emission regime.
• the correlation function reveals that patterns between subsequent pulses are similar (shown as peaks in the figure). Instead, in the bottom picture, no correlation is observable due to complete randomization of the phase between subsequent pulses.

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• Condensed Matter Physics & Semiconductors (AREA)
• Engineering & Computer Science (AREA)
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• Semiconductor Lasers (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

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• 2015
  • 2015-10-27 US US14/923,495 patent/US9710230B2/en active Active
• 2016
  • 2016-09-28 EP EP16781692.5A patent/EP3369148B1/en active Active
  • 2016-09-28 JP JP2018541494A patent/JP6945539B2/ja active Active
  • 2016-09-28 WO PCT/EP2016/073099 patent/WO2017071901A1/en not_active Ceased
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