Fast physical random bit generation based on an optoelectronic delay loop pumped by a semiconductor laser under a modulated optical feedback

We experimentally demonstrate multi-channel physical random bits (PRBs) generation by utilizing chaotic outputs from two linear polarization modes in a vertical-cavity surface-emitting laser (VCSEL) under a chaotic optical injection. The polarization-resolved chaotic signal is obtained with a master-VCSEL subject to optical feedback, and then injects into a slave-VCSEL for driving its two linear polarization modes into chaotic state. We analyze the influences of injection parameters on bandwidth, complexity, and the correlation of two-channel chaotic signals. By using the two chaotic signal outputs from the slave-VCSEL under optimized parameters as entropy sources, we have obtained the PRBs at the dual-channel rate of 160 Gbits/s by adopting the $m$ least significant bits extraction with logical exclusive-OR (XOR) post-processing. Further utilizing the $n$ -bit cross-merging method, the PRB at a rate of 320 Gbits/s could be obtained.

A new approach for high-speed physical random bit generation (RBG) based on broadband random optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In this scheme, a broadband random OEO based on Rayleigh scattering (RS) is employed as the entropy source of RBG. Compared with other broadband random OEOs which require an additional pump source, the optical signal output from the laser in the proposed scheme can realize excited Brillouin scattering as well as acting as an optical carrier. Benefiting from the introduction of randomly distributed feedback by RS, which breaks the limitation of the fixed loop length of the conventional chaotic OEO, the signals generated by the proposed broadband random OEO have random characteristics. Meanwhile, the generated signals exhibit wide and flat frequency spectrum characteristics due to the avoidance of semiconductor chaotic laser relaxation oscillations. The experimental results show the proposed RBG technique can generate physical random bits with a rate of up to 500 Gb/s which can fully pass the NIST test.

We demonstrate a random bit streaming system that uses a chaotic laser as its physical entropy source. By performing real-time bit manipulation for bias reduction, we were able to provide the memory of a personal computer with a constant supply of ready-to-use physical random bits at a throughput of up to 4 Gbps. We pay special attention to the end-to-end entropy source model describing how the entropy from physical sources is converted into bit entropy. We confirmed the statistical quality of the generated random bits by revealing the pass rate of the NIST SP800-22 test suite to be 65 % to 75 %, which is commonly considered acceptable for a reliable random bit generator. We also confirmed the stable operation of our random bit steaming system with long-term bias monitoring.

We demonstrate a physical random bit generation scheme based on a chaotic optoelectronic oscillator with silicon Mach-Zehnder modulator. The randomness of the 320Gbps sequence after two self-delay XOR operations is verified with NIST statistical tests.

We demonstrate physical random bit (PRB) generation from two chaotic optoelectronic oscillators (OEOs) with silicon Mach-Zehnder and microring resonator modulators. The carrier-injection modulation and the beam interference provide the nonlinearity for the OEO. We digitalize the chaotic waveforms from the two OEOs at 40GS/s with 8-bit resolution and use self-delay bitwise exclusive-or operation as a post-processing method. The randomness of the resulting 320Gbps PRB sequences is verified by the National Institute of Standards and Technology Special Publication 800-22 statistical tests. With the progress of silicon photonic circuits, there is a potential to fabricate a monolithic chaotic OEO chip for compact PRB generation.

We introduce a concept of noise robustness in dynamical systems with noise and argue that this concept is essential to guarantee the reliability of physical random bit generators (RBGs). As an example of promising physical RBGs we consider a chaotic laser system and show that it has the property of noise robustness with respect to changes in the temporal correlation of the noise source. Moreover, employing a simple model of tangent space dynamics, we give a theoretical interpretation of the numerical results and in particular show that the Lyapunov exponent determines a theoretical boundary of a noise-robust region in parameter space. These theoretical results are expected to be significant not only for chaotic lasers, but also for a broad class of chaotic dynamical systems with correlated noise.

We investigate post-processing functions with fixed-length inputs/outputs for reducing biases of random bits. When original random bits are i.i.d., biases of the post-processed sequences are polynomials in bias of the original bits, and a function is regarded as better if least degrees of those polynomials are larger. In this article we give upper and lower bounds of the optimal least degree for such post-processing functions, and in some cases determine the optimal degree precisely.

This paper reports the experimental investigation of two different approaches to random bit generation based on the chaotic dynamics of a semiconductor laser with optical feedback. By computing high-order finite differences of the chaotic laser intensity time series, we obtain time series with symmetric statistical distributions that are more conducive to ultrafast random bit generation. The first approach is guided by information-theoretic considerations and could potentially reach random bit generation rates as high as 160 Gb/s by extracting 4 bits per sample. The second approach is based on pragmatic considerations and could lead to rates of 2.2 Tb/s by extracting 55 bits per sample. The randomness of the bit sequences obtained from the two approaches is tested against three standard randomness tests (ENT, Diehard, and NIST tests), as well as by calculating the statistical bias and the serial correlation coefficients on longer sequences of random bits than those used in the standard tests.

A system is as secure as its weakest link. Current computing systems employ a multiple-layer approach to build a trusted environment. At the bottom of this multi-layer approach is a hardware root of trust which other layers build upon. It is important to assure this root of trust is secure and free from any weakness. Recently there is surge of research topics on hardware security. In this talk we first narrow the topic a bit and outline a more restricted definition of hardware security. Upon this tighter definition we try to explain why it is so hard to defend hardware attacks. We will give example from the recent hardware attacks. We, then, focus on a few topics related to hardware security including hardware Trojans and IC counterfeiting. We argue why it is very unlikely for a reputable foundry such as TSMC to plant them. On IC counterfeiting, there have been work on employing Physically Unclonable Function (PUF) to prevent counterfeiting. In this talk we will attempt to explain the difference between testing of these hardware security elements from testing of standard logic elements. We will also clarify that foundry is in the best position to work with customers directly in building these elements such as Physical Unclonable Functions (PUFs) and Physical Random Bits Generators (PRBGs).

The discrete multi-longitudinal mode structure and temporal periodic fluctuation are the intrinsic features of conventional lasers. However, longitudinal mode spacing limits the maximum resolution in high-resolution laser sensing systems. In addition, temporal periodic fluctuation reduces the security of secure communication and deteriorates the randomness in fast physical random bit generation. Therefore, it still remains an open challenge to realize a laser source without discrete longitudinal mode and temporal periodic fluctuation. Here, a modeless Raman fiber laser (RFL) with high efficiency was demonstrated. The output cavity mirror adopts a fiber Bragg grating with ultralow reflectance of −27dB. Due to the modulation instability, the discrete multi-longitudinal modes in the RFL gradually broaden with the increase of intracavity Stokes wave power and eventually fully overlap. At high power levels, the RFL no longer has discrete longitudinal modes like a conventional laser but generates a quasi-continuous spectrum. Benefiting from the modeless nature, the RFL can achieve extremely low relative intensity noise, favorable temporal stability, and rather low coherence. Modeless RFLs are expected to be ushered as ideal light sources into secure communication, optical sensing, and optical imaging.

In the present work a photonic integrated circuit (PIC) that emits broadband chaotic signals is employed for ultra-fast generation of true random bit sequences. Chaotic dynamics emerge from a DFB laser, accompanied by a monolithic integrated 1-cm long external cavity (EC) that provides controllable optical feedback. The short length minimizes the existence of external cavity modes, so flattened broadband spectra with minimized intrinsic periodicities can emerge. After sampling and quantization--without including optical de-correlation techniques and using most significant bits (MSB) elimination post-processing--truly random bit streams with bit-rates as high as 140 Gb/s can be generated. Finally, the extreme robustness of the random bit generator for adaptive bit-rate operation and for various operating conditions of the PIC is demonstrated.

Random bit generation (RBG) with chaotic semiconductor lasers has been extensively studied because of its potential applications in secure communications and high-speed numerical simulations. Researchers in this field have mainly focused on the improvement of the generation rate and the compactness of the random bit generators. In this paper, we experimentally demonstrate the existence of two regimes of fast RBG using a single chaotic laser subjected to delayed optical feedback: the first one is based on the extraction of all min-entropy contained in each random sample, and the second one is to demonstrate a possibility of increasing the generation rate by extracting 55 bits from each variable.

A simple schemefor generating chaotic signals with concealed time-delay signature (TDS) is proposed and experimentally demonstrated. The architecture of the system is based on a semiconductor laser (SL) under multi-path optical feedback (MPOF) provided by a 2 × 2 fiber coupler (FC) and a fiber mirror (FM). The results show that SLs with MPOF are more beneficial for achieving TDS suppressed chaotic output than those with single optical feedback (SOF) systems. In addition, the TDS of the chaotic signal generated by the SL under MPOF is insensitive to the length deviation of the feedback cavities, and therefore such a scheme is convenient for practical application. Furthermore, the influence of FC coupling ratio in the MPOF module, feedback strength, and bias current of the SL on the TDS is comprehensively studied. By selecting suitable parameters, the TDS of the chaotic signal generated by the SL under MPOF can be completely concealed. Finally, permutation entropy (PE) is adopted to evaluate the complexity of the generated chaotic signal, and the result demonstrates that the suppression of TDS does not lead to the degradation of complexity for the proposed scheme.

This paper explores the design and performance evaluation of an all-optical combinational logic network. The proposed optical digital link generates AND logic operation along with exclusive OR logic operations concurrently in a single unit. Numerical simulation for the applied data inputs and consequence output has been successfully accomplished. Accordingly, desired outputs for the combinational network—the AND logic, the exclusive OR logic—have been verified at the 20 Gbps of data rate. Numerical simulations for the different key design parameters, for instance, current injection efficiency and pump current of semiconductor optical amplifier and the variation in the operating data rates up to 20 and 50 Gbps have been carried out. It has showed very good extinction ratio (>10 dB) performance. The proposed design is compact and avoids frequent optoelectronic conversions, and it is well supportive to design forthcoming all-optical complex computing networks.

In this paper, we investigate the possibility of using optical injection to efficiently suppress the time-delay (TD) signatures of chaotic signals in a large experimentally accessible parameter range of semiconductor ring lasers (SRLs). We also study how this optical injection can improve the signal bandwidths. The injection signal is obtained from a master SRL with either optical self- or cross-feedback. For optical self-feedback configurations, it is found that the suppression of TD signatures is similar to what has been found in injected Fabry–Perot semiconductor lasers, i.e., narrow range of parameters with respect to the detuning and injection strengths. For cross-feedback configurations, however, the TD signatures can be suppressed in a wide range of parameters; meanwhile, the bandwidths are significantly improved for the same range of parameters. This is particularly useful for the security in chaos-based communications and also for generating random bits with improved properties.