Satoshi Sunada

Fast Random Number Generation With Bandwidth-Enhanced Chaotic Semiconductor Lasers at 8

We propose a scheme for fast random number generation with bandwidth-enhanced chaotic semiconductor lasers. Chaotic laser intensity output and its time-delayed signal are sampled at 50 GigaSample per second and converted into eight-bit values. The order of the eight-bit samples of the time-delayed signal is reversed, and bitwise exclusive-or operation is executed between the bit-order-reversed samples and the original eight-bit samples. With this method, it is not necessary to eliminate any of the bits in eight-bit samples in order to obtain good-quality random bit sequences. The equivalent generation rate of 8×50 Gb/s is achieved in an experiment using bandwidth-enhanced chaotic semiconductor lasers.

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We report a novel chaos semiconductor laser chip in which a distributed feedback (DFB) laser, two semiconductor optical amplifiers (SOAs) and a photodiode (PD) are monolithically integrated with a passive ring waveguide. The ring-type structure with the two separate SOAs achieves stronger delayed optical feedback compared to previous chaos laser chips which use linear waveguide and facet-reflection. The integrated PD allows efficient detection of the optical signal with low optical loss. A rich variety of dynamical behaviors and optical signals can be selectively generated via injection currents to the two separate SOAs. In particular, the strong optical feedback makes possible the generation of strong broadband optical chaos, with very flat spectrum of ±6.5 dB up to 10 GHz. The stability and quality of the chaotic mode is demonstrated using strict statistical tests of randomness applied to long binary sequences extracted by sampling the optical intensity signal.

50 Gb/s

We theoretically and numerically study the effect of backscattering on rotating ring lasers by employing the Maxwell-Bloch equations. We show that frequency shifts due to the Sagnac effect incorporating the effect of backscattering can be observed without lock-in phenomenon, if the strength of backscattering originating in the bumps of the refractive index is larger than a certain value. It is also shown that the experimental results corresponding to the theoretical ones can actually be obtained by using a semiconductor fiber-optic ring laser gyroscope.

Chaos laser chips with delayed optical feedback using a passive ring waveguide.

We generate random bit sequences from chaotic temporal waveforms by using photonic integrated circuits (PICs) with different external cavity lengths. We investigate the condition for generating random bits at different sampling rates of single-bit generation method with the PICs. We succeed in generating certified random bit sequences by using the PIC with 3, 4, 5, or 10-mm-long external cavity, whereas random bits cannot pass all the statistical tests of randomness when the PIC with 1 or 2 mm-long external cavity is used.

Ring-laser gyroscope without the lock-in phenomenon

We report the Sagnac effect in resonant microcavities. The Sagnac effect is the phase and frequency difference between two counter propagating laser beams in a rotating ring resonator, and has been studied for a long time. It forms the basis for the optical gyroscopes, such as ring laser gyroscope or fiber optic gyroscopes. Conventional theoretical approach for the Sagnac effect has been derived from the assumption that the light propagates one-dimensionally and the wavelength of the light is typically much smaller than the cavity length. However, nowadays, micro-fabrication techniques are developed enough that the cavity size can approach the size of the wavelength of the light. The conventional formalism for the Sagnac effect, therefore, breaks down and needs to be replaced. We derive the Sagnac effect in resonant microcavities theoretically and numerically without the conventional assumption and show that the frequency shift due to the Sagnac effect occurs as a threshold phenomenon for rotation velocity in a rotating microcavity by employing perturbation theory typically used in quantum mechanics. The threshold exists even in the absence of the backscattering, which causes the lock-in phenomenon, and depends on the geometric shape and the symmetry of resonant cavities. It is also shown that the eigenfunctions of a rotating microcavity become rotating waves above the threshold while they are standing waves below the threshold. Our theoretical approach can be applied to the resonant cavities of arbitrary shapes and can make it possible to design compact optical gyroscopes that have a low threshold

Fast physical random bit generation with photonic integrated circuits with different external cavity lengths for chaos generation

We experimentally show that a random optical pulse train can be generated by modulating a bistable semiconductor ring laser. When the ring laser is switched from the monostable to the bistable regime, it randomly selects one of two different stable unidirectional lasing modes, clockwise or counterclockwise modes. Non-deterministic random pulse sequences are generated by driving the switch parameter, the injection current, with a periodic pulse signal. The origin of the nondeterministic randomness is the amplified spontaneous emission noise coupled to the counter-propagating lasing modes. The statistical randomness properties are optimized by adjusting the relative strength of amplified spontaneous emission noise sources for the two lasing modes. It is also shown that it is possible to generate optical pulse sequences which pass a standard suite of statistical randomness tests.

Sagnac Effect in Resonant Microcavities

We present an experimental method for directly observing the amplification of microscopic intrinsic noise in a high-dimensional chaotic laser system, a laser with delayed feedback. In the experiment, the chaotic laser system is repeatedly switched from a stable lasing state to a chaotic state, and the time evolution of an ensemble of chaotic states starting from the same initial state is measured. It is experimentally demonstrated that intrinsic noises amplified by the chaotic dynamics are transformed into macroscopic fluctuating signals, and the probability density of the output light intensity actually converges to a natural invariant probability density in a strongly chaotic regime. Moreover, with the experimental method, we discuss the application of the chaotic laser systems to physical random bit generators. It is experimentally shown that the convergence to the invariant density plays an important role in nondeterministic random bit generation, which could be desirable for future ultimate secure communication systems.

Random optical pulse generation with bistable semiconductor ring lasers

We show that, even when the eigenmodes of an optical cavity are wave chaotic, degenerate eigenfrequencies of those modes split into different frequencies due to the rotation of the cavity. The frequency difference is proportional to the angular velocity, although the splitting eigenmodes are still wave chaotic and do not correspond to any unidirectionally rotating waves.

Noise amplification by chaotic dynamics in a delayed feedback laser system and its application to nondeterministic random bit generation

We study theoretically and numerically the effect of rotation on resonant frequencies of microcavities in a rotating frame of reference. Cavity rotation causes the shifts of the resonant frequencies proportional to the rotation rate if it is larger than a certain value. Below the value, a region of rotation rate exists where there is no resulting the frequency shifts proportional to the rotation rate. We show that designing cavity symmetry as C(nv) (n >/= 3) can eliminate this region.

Wave chaos in rotating optical cavities.

We investigated the lasing modes of quasi-stadium laser diodes that have confocal cavity geometries, with stripe electrode contacts formed either along the cavity axis or a diamond-shaped trajectory. It was clearly demonstrated that by using narrow electrode contact patterns of 2 μm width, the lowest-order axial and ring modes were excited selectively. On the other hand, the second-lowest-order axial and ring modes were excited by using broad electrode patterns of 14 μm width. Experimentally obtained far-field patterns for lasers with broad and narrow electrode contact patterns agree very well with the simulation results obtained using an extended Fox-Li mode calculation method.