Laser chip and random number generation system

Abstract

The application provides a laser chip and a random number generation system, wherein the laser chip is provided with two laser regions, the two regions have a free running wavelength difference, and the two regions are optically mutually coupled by a common sampling grating to generate chaotic light signals; the generated chaotic signals can completely eliminate the time delay characteristics, so that an attacker cannot infer the system delay parameters through autocorrelation analysis or phase space reconstruction, thereby significantly improving the anti-prediction attack capability of the random number at the physical layer. On this basis, the random number generation system is combined with an optimized delay subtraction and multi-bit extraction post-processing algorithm, and a random number generation rate of 400 Gb / s is successfully realized; the system has the advantages of compact structure, no time delay characteristics, strong environmental robustness and the like, and has a wide application prospect in the fields of quantum key distribution, high-speed data encryption, optical fiber sensing encryption and large-scale scientific calculation.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic integration technology, specifically relating to a laser chip and a random number generation system. Background Technology

[0002] In modern cryptography, quantum communication, large-scale numerical simulations (such as the Monte Carlo method), and neural network training in artificial intelligence, high-quality random numbers are the cornerstone of ensuring system security and computational accuracy. Based on their generation mechanisms, random numbers are mainly divided into pseudo-random numbers (PRNs) and physically random numbers (PRNs). Pseudo-random numbers are typically generated by deterministic mathematical algorithms (such as linear congruential methods). While they have advantages such as long periods and fast computation speeds, they are inherently predictable. Once the algorithm is leaked or the initial seed is cracked, the security of the entire system will be compromised. In contrast, physically random numbers originate from unpredictable physical processes (such as thermal noise and quantum fluctuations), possessing true unpredictability and aperiodicity, making them the "ultimate weapon" in the field of information security.

[0003] Currently, the generation rate of physical random numbers has become a bottleneck restricting their application in high-speed communications (such as 400G / 800G Ethernet). Traditional random number generators based on electronic thermal noise are limited by electronic bottlenecks, and their rates are usually difficult to exceed the Gb / s level. Optical random number generation technology, which utilizes the ultra-high-speed motion characteristics of photons, offers a possibility for overcoming this bottleneck. In particular, the Physical Random Number Generator (PRBG) based on Optical Chaos, which utilizes chaotic signals generated by semiconductor lasers under nonlinear dynamics, has advantages such as large bandwidth, high complexity, and unpredictability.

[0004] However, most existing PRBG systems based on optical chaos are built using discrete components, such as external cavity feedback systems constructed with external mirrors or fiber gratings, or optical injection locking using two independent lasers. These discrete systems have significant drawbacks: First, they are bulky and difficult to align optically, making them unsuitable for the miniaturization requirements of modern electronic devices. Second, discrete components are extremely sensitive to environmental temperature and vibration; even minor environmental disturbances can cause changes in the optical path phase, affecting the stability of the chaotic signal and potentially leading to system failure. Finally, traditional external cavity feedback chaotic systems often exhibit a significant time-delay signature (TDS), which provides attackers with an opportunity to predict random numbers by reconstructing the phase space, reducing system security.

[0005] To address these issues, the academic community has recently begun exploring solutions based on photonic integrated circuits (PICs). For example, microcavity soliton optical frequency combs or vertical-cavity surface-emitting laser (VCSEL) arrays are used to generate random numbers. While these solutions offer improvements in integration density, they still face challenges such as complex manufacturing processes (e.g., requiring electron beam lithography), high costs, and difficulties in eliminating time delay characteristics. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a laser chip and a random number generation system to solve the time delay problem of existing PRBG systems based on photonic chaos.

[0007] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0008] A laser chip has two laser regions with a free operating wavelength difference between them. The two regions are optically injected and coupled together through a common sampling grating to generate a chaotic light signal.

[0009] Furthermore, the free-running wavelength difference is 0.3 nm.

[0010] Furthermore, from bottom to top, it includes: a substrate layer, a buffer layer, a lower cladding layer, a lower confinement layer, a multiple quantum well layer, an upper confinement layer, an electron blocking layer, a buffer layer, a grating layer, a spacer layer, an etching barrier layer, a waveguide layer, a lattice matching layer, and an ohmic contact layer;

[0011] The waveguide layer, lattice matching layer, and ohmic contact layer constitute a ridge waveguide structure with a ridge width of 2 μm. Two laser regions are provided on the ridge waveguide structure, each with a length of 450 μm. An electrically isolated trench with a width of 5 μm and a depth reaching into the waveguide layer is provided between them.

[0012] Furthermore, both the front and rear cavity surfaces of the chip are coated with antireflection films, and the reflectivity of the antireflection films is less than 1%.

[0013] The chip is packaged in a butterfly package and contains a thermoelectric cooler and a thermistor.

[0014] Furthermore, the process involves preparing the material using a reconstructed equivalent chirp technique, including:

[0015] Step 1, Epitaxial Growth: Using metal-organic chemical vapor deposition, a buffer layer, a lower cladding layer, a lower confinement layer, a multi-quantum well layer, an upper confinement layer, an electron blocking layer, a buffer layer, and a grating layer are sequentially grown on a 2-inch n-type InP substrate. The active region is designed with a center wavelength of 1550 nm, and the number of quantum wells is 5. The material system is InGaAsP / InP.

[0016] Step 2, fabrication of the sampling grating:

[0017] Step 2.1: Coat the grating layer with photoresist, and define a uniform seed grating on the photoresist by holographic exposure. The seed grating period is 240 nm.

[0018] Step 2.2: Define the sampling structure using contact exposure, with a sampling period P of 4.244 μm;

[0019] Step 3, Secondary epitaxy and ridge waveguide etching: First, metal-organic chemical vapor deposition is used to grow a spacer layer, an etching barrier layer, a waveguide layer, a lattice matching layer and an ohmic contact layer in sequence; then, standard photolithography and inductively coupled plasma etching are used to form the ridge waveguide structure.

[0020] Step 4, Electrical isolation and electrode fabrication:

[0021] Step 4.1: For the ridge waveguide structure, between the two predetermined laser regions, the ohmic contact layer and the lattice matching layer are penetrated by ICP etching.

[0022] Step 4.2: Deposit Ti / Pt / Au metal electrodes on the ohmic contact layer of the two laser regions using photolithography and lift-off processes;

[0023] Step 5, Cavity Surface Coating and Packaging: After chip cleaving, antireflection films are deposited on both the front and rear cavity surfaces. Finally, the chip is hermetically sealed in a butterfly package, housing a thermoelectric cooler and a thermistor.

[0024] A random number generation system, comprising:

[0025] Chaotic laser: Composed of the laser chip described above, used to generate chaotic light signals;

[0026] DC bias drive circuit: used to provide DC bias current to the two laser regions;

[0027] Optical coupling and transmission module: used for transmitting chaotic optical signals;

[0028] Photoelectric detection module: used to receive chaotic light signals and linearly convert them into analog electrical signals;

[0029] Data acquisition and post-processing module: Samples analog electrical signals and generates random numbers.

[0030] Furthermore, an optical isolator is installed in the optical path to prevent reflected light from being fed back to the laser chip.

[0031] Further, generate random numbers as follows:

[0032] The original chaotic data sequence X(t) is obtained by sampling the analog electrical signal;

[0033] The difference data sequence Y(t) = X(t) - X(t-τ) is obtained through difference operation, where X(t-τ) is the data sequence after a delay time τ;

[0034] A multi-bit extraction strategy is adopted to extract the lowest number of bits from each sampling point in Y(t) to form a random number bit stream.

[0035] Furthermore, the analog electrical signal is continuously sampled with 8-bit quantization precision to form X(t), and the lowest 4 bits of Y(t) are extracted from each sampling point to form a random number bit stream.

[0036] Furthermore, the delay time point with the smallest autocorrelation function value and cross-correlation coefficient of sequence X(t) is selected as the delay time τ, and the delay time τ = 1 ns.

[0037] The beneficial effects of this invention are as follows:

[0038] (1) The present invention provides a laser chip containing two laser regions, which are optically mutually injected and coupled through a common sampling grating structure, and the free operating wavelength difference between the two is 0.3nm; by eliminating external optical components through the above monolithic integrated structure, the environmental sensitivity problem is fundamentally solved; the chaotic signal generated by this chip can completely eliminate the time delay feature (TDS), making it impossible for attackers to infer the system delay parameters through autocorrelation analysis or phase space reconstruction, thereby significantly improving the anti-prediction attack capability of random numbers at the physical layer.

[0039] (2) The laser chip of the present invention is fabricated by using REC technology instead of electron beam lithography and using standard InP process line for large-scale production, which is low cost; the monolithic integrated structure makes the system free from optical alignment, and has strong resistance to vibration and temperature drift, making it suitable for industrial applications.

[0040] (3) The front cavity surface and the rear cavity surface of the laser chip of the present invention are coated with anti-reflection film layers. The reflectivity of the anti-reflection film layer is controlled to be below 1% in order to eliminate random phase interference introduced by Fresnel reflection of the cavity surface.

[0041] (4) Based on the above-mentioned laser chip, the present invention also provides a random number generation system, which combines an optimized delay subtraction and multi-bit extraction post-processing algorithm to successfully achieve a random number generation rate of 400Gb / s. The system has significant advantages such as compact structure, no time delay, and strong environmental robustness, and has broad application prospects in quantum key distribution, high-speed data encryption, fiber optic sensing encryption and large-scale scientific computing.

[0042] (5) The random number generation system of the present invention can eliminate the non-Gaussianity and asymmetry of data distribution by adjusting and optimizing the delay time, and effectively eliminate the original bias. Attached Figure Description

[0043] Figure 1 This is a diagram of the laser chip hierarchy structure of the present invention;

[0044] Figure 2 This is a three-dimensional structural diagram of the laser chip of the present invention;

[0045] Figure 3 These are actual micrographs of the laser of this invention;

[0046] Figure 4 This is a schematic diagram of the random number generation system of the present invention;

[0047] Figure 5 The present invention provides spectral data of the laser chip under different current excitation conditions.

[0048] Figure 6 This is the test data of the chaotic signal of the random number generation system of this invention;

[0049] Figure 7 This describes the random number distribution of the random number generation system of the present invention.

[0050] Figure 8 The results are from the NIST test of the random number system of this invention.

[0051] Figure label:

[0052] 1-Substrate; 2-Buffer layer; 3-Lower cladding layer; 4-Lower confinement layer;

[0053] 5-Multiple quantum well layer; 6-Upper confinement layer; 7-Electron blocking layer; 8-Buffer layer;

[0054] 9-Raster layer; 10-Spacer layer; 11-Etching barrier layer; 12-Waveguide layer;

[0055] 13-Lattice matching layer; 14-Ohmic contact layer. Detailed Implementation

[0056] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein similar or identical reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0057] I. Integrated Mutual Injection DFB Laser Chip

[0058] 1. Chip Structure

[0059] This invention employs an integrated cross-injection DFB (distributed feedback) laser chip as the core component of the random number generation system. The chip's structure is as follows: Figure 1 and Figure 2 As shown:

[0060] From bottom to top, it includes: substrate layer 1, buffer layer 2, lower cladding layer 3, lower confinement layer 4, multiple quantum well layer 5, upper confinement layer 6, electron blocking layer 7, buffer layer 8, grating layer 9, spacer layer 10, etch barrier layer 11, waveguide layer 12, lattice matching layer 13, and ohmic contact layer 14.

[0061] The waveguide layer 12, lattice matching layer 13, and ohmic contact layer 14 form a ridge waveguide structure with a ridge width of 2 μm, serving as the laser region. The chip contains two laser regions, denoted as LD1 and LD2, each with a physical length of 450 μm, separated by an electrically isolated trench. This trench has a width of 5 μm (the distance between LD1 and LD2) and extends into the waveguide layer 12, effectively blocking the lateral diffusion of charge carriers and enabling independent electrical drive of the two laser regions.

[0062] Figure 3 The image shown is a micrograph of the fabricated chip, clearly showing the two laser regions and the electrical isolation trench between them.

[0063] 2. Preparation method

[0064] The chip described above is fabricated using the Reconstructed Equivalent Chirp (REC) technique. The specific fabrication steps are as follows:

[0065] Step 1, one-time epitaxial growth

[0066] Metal-organic chemical vapor deposition (MOCVD) was used to sequentially grow a buffer layer 2, a lower cladding layer 3, a lower confinement layer 4, a multi-quantum-well layer 5, an upper confinement layer 6, an electron blocking layer 7, a buffer layer 8, and a grating layer 9 on a 2-inch n-type InP substrate (corresponding to substrate layer 1). The active region was designed with a center wavelength of 1550 nm, and the number of quantum wells was 5. The material system was InGaAsP / InP.

[0067] Step 2, Fabrication of the sampling grating

[0068] A sampling grating is fabricated on grating layer 9. Unlike traditional electron beam lithography, this invention employs reconstructed equivalent chirp (REC) technology to achieve precise equivalent modulation of the grating phase. This process is fully compatible with standard semiconductor laser production lines, avoiding the use of expensive electron beam direct-write equipment and significantly reducing chip manufacturing costs.

[0069] Step 2.1: Coat photoresist on grating layer 9, and define a uniform seed grating on the photoresist using holographic exposure technology. The seed grating period is 240 nm, corresponding to the 0th order Bragg wavelength of 1635 nm.

[0070] Step 2.2 defines the sampling structure using micrometer-precision contact exposure, with a sampling period P designed to be 4.244 μm, ensuring that the Bragg wavelength of the +1st-order sub-grating falls within the 1550 nm band. A phase-shifting structure is embedded in the sampling grating, and the phase shift ΔP is equivalently generated as a π phase shift using the formula m = 2πmΔP / P, thereby guaranteeing the single-longitudinal-mode operating characteristics of the laser.

[0071] Step 3, Secondary epitaxy and ridge waveguide etching

[0072] After the sampling grating etching is completed, a second MOCVD epitaxy is performed to grow a spacer layer 10, an etch barrier layer 11, a waveguide layer 12, a lattice matching layer 13, and an ohmic contact layer 14 in sequence; then, a ridge waveguide structure with a ridge width of 2 μm is formed by using standard photolithography and inductively coupled plasma (ICP) etching processes.

[0073] Step 4, Electrical isolation and electrode fabrication

[0074] Step 4.1: For the ridge waveguide structure, between the two predetermined laser regions, ICP etching is used to penetrate the ohmic contact layer 14 and the lattice matching layer 13, extending into the waveguide layer 12, thereby effectively blocking the lateral diffusion of charge carriers and realizing independent electric drive of the two laser regions.

[0075] Step 4.2: Deposit Ti / Pt / Au metal electrodes on the ohmic contact layer 14 of the two laser regions using photolithography and lift-off processes.

[0076] Step 5, Cavity surface coating and encapsulation

[0077] After chip cleaving, antireflection coatings (AR films) are deposited on both the front and rear cavity surfaces, with reflectivity controlled below 1% to eliminate random phase interference introduced by Fresnel reflections at the cavity surfaces, ensuring that chaotic signals are dominated by the mutual injection dynamics process. Finally, the chip is hermetically packaged in a butterfly package, incorporating a thermoelectric cooler (TEC) and a thermistor for precise temperature control.

[0078] II. Random Number Generation System

[0079] 1. System Composition

[0080] include:

[0081] (1) Chaotic laser: a laser based on the above-mentioned integrated inter-injected DFB laser chip, used to generate chaotic light signals. Based on the built-in TEC and thermistor, the heat sink temperature of the chip is controlled to be constant at 25±1℃; temperature stability is crucial for the repeatability of chaotic dynamics.

[0082] (2) DC bias drive circuit: Two low-noise precision current sources (such as ILX Lightwave LDX-3620B) are used to provide independently adjustable DC bias currents to LD1 and LD2 respectively. The current source output accuracy is 0.1 mA, ensuring the stability and accuracy of the drive current.

[0083] (3) Optical coupling and transmission module: The chaotic optical signal generated by the output chip is coupled using a tapered single-mode fiber, with a coupling efficiency of about 40%. An optical isolator (isolation degree > 35 dB) is connected in the optical path to prevent the reflected light from subsequent optical components from feeding back to the laser chip and interfering with the chaotic oscillation state.

[0084] (4) Photodetector module: A high-speed PIN photodetector (Finisar XPDV2120R) is used to receive chaotic optical signals and linearly convert them into analog electrical signals. Its 3 dB bandwidth is 25 GHz, which can completely preserve the high-frequency components of the chaotic signal.

[0085] (5) Data Acquisition and Post-processing Module: This module includes a high-speed real-time oscilloscope (Tektronix DPO73304DX) and a field-programmable gate array (FPGA) processing board. The oscilloscope has a built-in analog-to-digital converter (ADC) with a sampling rate of 100 GSa / s and a quantization precision of 8 bits. The FPGA is used to execute delay subtraction and bit extraction algorithms in real time to generate the final required random numbers; it also includes a data buffer unit and a real-time testing unit for online monitoring of randomness while generating random numbers.

[0086] like Figure 4 The diagram illustrates the working principle of the random number generation system described above. First, a chaotic laser generates a chaotic optical signal, which is then transmitted via a tapered single-mode fiber to a photodetector. This signal is converted into a chaotic analog electrical signal and finally transmitted to an oscilloscope (and subsequently an FPGA) for processing to obtain random numbers. To avoid interference from reflected light, an optical isolator is placed in the optical path. For testing, verification, or debugging, a spectrometer and a spectrum analyzer can be connected to the optical and electrical paths respectively to read the optical and electrical signals.

[0087] 2. Testing and Verification of Chaotic (Optical / Electrical) Signals

[0088] 2.1 Determination of free-running wavelength

[0089] First, the bias current of LD2 was set to a very low value (approximately 16 mA) that could only compensate for material absorption, and the bias current of LD1 was set to 49 mA, at which point LD1 was in lasing mode. The spectrum of LD1 was recorded using a spectrometer with a resolution of 0.02 nm (Yokogawa AQ6370D), and the free-running center wavelength of LD1 was measured to be 1539.85 nm. Figure 5 (a) is shown by the blue curve.

[0090] Then, using symmetrical operation, the bias current of LD1 was reduced to 16mA, and the bias current of LD2 was increased to 46mA. The free-running center wavelength of LD2 was measured to be 1539.55nm. Figure 5 As shown by the red curve in (a), the free-running wavelength difference between the two lasers is precisely locked at 0.3 nm, which perfectly matches the design value of the sampling period of the chip's REC grating.

[0091] 2.2, Chaotic State Induction

[0092] When the bias currents of LD1 and LD2 are simultaneously set to 49mA and 46mA respectively, the two lasers enter a state of strong chaotic oscillation under the mutual injection coupling mechanism. Figure 6 The black curve in (a) shows the spectrum in this state. The spectrum is significantly broadened and the top tends to be flat, indicating that mutual injection leads to intense mode competition and enhanced nonlinear dynamics.

[0093] 2.3 Radio Frequency (RF) Spectrum Analysis

[0094] The chaotic electrical signal output from the photodetector is connected to an electrical spectrum analyzer, and the radio frequency spectrum of the chaotic signal is measured as follows: Figure 6 As shown in (b), the red curve in the figure represents the RF spectrum under chaotic conditions, and the black curve represents the system noise floor. The frequency range corresponding to 80% of the energy in the RF spectrum is defined as the chaotic bandwidth. Calculations show that the 80% energy bandwidth of this chaotic signal reaches 20.1 GHz. Such a wide bandwidth provides a sufficient entropy source for ultra-high-speed random number generation. Furthermore, Figure 6 (c) shows the AC waveform of the chaotic laser.

[0095] 2.4 Analysis of Autocorrelation Characteristics and Time Delay Features

[0096] The time series of chaotic signals were acquired using an oscilloscope, and their autocorrelation function (ACF) was calculated. The results are as follows: Figure 6 As shown in (d), the main plot shows a single correlation peak at zero delay, while at any non-zero delay, the autocorrelation value rapidly decays to near noise levels. Figure 6(d) The inset plot shows the complete ACF curve over a 500 ns time range. Except for zero delay, no significant secondary correlation peaks were observed. This result demonstrates that the chaotic signal generated by the monolithically inter-injected DFB laser of this invention completely eliminates the time delay characteristic (TDS). This contrasts sharply with traditional discrete external cavity feedback chaotic systems, which exhibit significant periodic correlation peaks due to the external cavity round-trip time. The elimination of TDS means that attackers cannot infer the system delay parameters through autocorrelation analysis or phase space reconstruction, thus significantly improving the resistance to predictive attacks on random numbers at the physical layer.

[0097] 3. Implementation of Random Number Generation and Post-processing Algorithms

[0098] Based on the above chaotic signal, the final required physical random number bit stream is generated according to the following steps:

[0099] Step 1, Data Collection

[0100] The oscilloscope's ADC continuously samples the chaotic analog electrical signal at a sampling rate of 100 GSa / s and 8-bit quantization precision, obtaining the original chaotic data sequence X(t). The amplitude probability density function (PDF) of the original data is as follows: Figure 7 As shown in (a), it exhibits a typical asymmetric distribution with a certain peak characteristic. If this non-Gaussian, asymmetric distribution is directly used for random position extraction, it will lead to serious statistical bias.

[0101] Step 2, Post-processing after delay subtraction

[0102] To eliminate the asymmetry and weak periodicity of the original data distribution, this invention implements a delayed subtraction algorithm. Specifically, the original data sequence X(t) and the data sequence X(t-τ) after a specific delay time τ are subtracted to obtain the difference data sequence:

[0103] Y(t) = X(t) - X(t-τ)

[0104] The selection of the delay time τ is crucial to the algorithm's performance. Based on theoretical analysis and experimental verification, weak periodicity can be effectively eliminated when the cross-correlation coefficient between the chaotic signal and its delayed replica is less than 0.007. Figure 6 The autocorrelation curve of (d) shows that the cross-correlation coefficient is much lower than 0.007 after a delay of 1 ns. Therefore, the optimal delay time τ = 1 ns is selected in this embodiment.

[0105] Figure 7 (b) shows the intensity distribution of the differential data after delay subtraction, where the probability density function is transformed into a highly symmetrical bimodal structure, effectively eliminating the original bias.

[0106] Step 3, Multi-bit Extraction and Normalization

[0107] To fully utilize the 8-bit high quantization precision of the ADC and avoid the waste of entropy sources caused by single-bit extraction, this invention adopts a multi-bit extraction strategy. For each 8-bit binary sample in the differential data sequence Y(t), its lowest 4 significant bits (4-LSBs) are extracted.

[0108] The basis for selecting LSBs is that the high-frequency random fluctuations of chaotic signals mainly contribute to the lower bits of the quantized data, while the higher bits reflect the slowly varying envelope of the signal and may retain weak periodicity. After delay and subtraction, the distribution of "0" and "1" in the lower bits tends to be uniform.

[0109] like Figure 7 As shown in (c), after extracting 4-LSBs, the probability distribution of the resulting 4-bit binary code is extremely close to the ideal uniform distribution, and the probability deviation of each code value is within ±0.001.

[0110] Since each sampling point can extract 4 random bits, at a sampling rate of 100 GSa / s, the final physical random number generation rate reaches 4 bits × 100 GSa / s = 400 Gb / s. Furthermore, Figure 7 (d) shows the autocorrelation plot of the generated bitstream over a delay of 1 ns, with the correlation value consistently remaining within a certain range. Near the theoretical lower limit (n=10) 6 (where is the sequence length), indicating that there is no statistical correlation between bits.

[0111] 4. Randomness verification

[0112] To rigorously verify the statistical quality of the generated random sequences, the SP 800-22 statistical test suite published by the National Institute of Standards and Technology (NIST) was used for standard testing. The test parameters were set as follows: 1000 random sequences of 1 Mbit length were used as samples, with a significance level of α = 0.01. Under these conditions, two criteria must be met to pass each test:

[0113] (1) The uniformity of P-values ​​is greater than 0.0001;

[0114] (2) The proportion of sequences that passed the test fell within the confidence interval of 0.99 ± 0.0094392.

[0115] Figure 8The NIST test results for the random sequence in this embodiment are summarized. In the 15 core statistical tests (including frequency test, intra-block frequency test, run test, longest run test, binary matrix rank test, discrete Fourier transform test, non-overlapping module matching test, overlapping module matching test, Maurer general statistical test, linear complexity test, sequence test, approximate entropy test, summation test, random walk test, and random walk state frequency test), the p-values ​​for all items were greater than 0.0001, and the pass rate was within the 99% confidence interval. These results consistently demonstrate that the 400Gb / s random number sequence generated by this system possesses true physical randomness, meeting the high standards required for cryptographic applications.

[0116] 5. System robustness and environmental adaptability verification

[0117] To verify the robustness of the system under non-ideal environments, an environmental temperature perturbation experiment was conducted. The TEC setpoint temperature of the laser chip was gradually modulated from 25℃ in increments of ±0.5℃, while simultaneously monitoring the chaotic RF bandwidth and the proportion of random numbers passing the NIST test. Experimental results show that within a temperature fluctuation range of ±0.5℃, the change in chaotic RF bandwidth is less than 0.5GHz, and the NIST test pass rate for the random number sequence remains consistently 100%. This is attributed to two factors:

[0118] Firstly, the butterfly packaging and TEC closed-loop control ensure a highly stable chip junction temperature;

[0119] Secondly, the delay-subtraction algorithm itself has self-calibration capability for the slow power drift of chaotic signals, further enhancing the system's immunity to residual environmental disturbances.

[0120] In summary, the ultrafast physical random number generation system based on an integrated cross-injected DFB laser of this invention, utilizing a low-cost, high-performance chaotic light source prepared by REC technology, combined with an optimized delay subtraction and multi-bit extraction post-processing algorithm, successfully achieved a random number generation rate of 400 Gb / s. The system possesses significant advantages such as compact structure, zero time delay, and strong environmental robustness, and has broad application prospects in fields such as quantum key distribution, high-speed data encryption, fiber optic sensing encryption, and large-scale scientific computing.

[0121] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0122] This invention is not limited to the embodiments described above. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of this invention are within the scope of protection of this invention.

Claims

1. A laser chip, characterized in that: The system consists of two laser regions with a free-running wavelength difference between them. The two lasers are optically inter-injected and coupled through a common sampling grating to generate a chaotic optical signal.

2. The laser chip according to claim 1, characterized in that: The free-running wavelength difference is 0.3 nm.

3. The laser chip according to claim 1, characterized in that: From bottom to top, it includes: substrate layer (1), buffer layer (2), lower cladding layer (3), lower confinement layer (4), multiple quantum well layer (5), upper confinement layer (6), electron blocking layer (7), buffer layer (8), grating layer (9), spacer layer (10), etch barrier layer (11), waveguide layer (12), lattice matching layer (12) and ohmic contact layer (14); The waveguide layer (12), lattice matching layer (13) and ohmic contact layer (14) constitute a ridge waveguide structure with a ridge width of 2μm. Two laser regions are provided on the ridge waveguide structure, each with a length of 450μm. An electrically isolated trench with a width of 5μm and a depth reaching into the waveguide layer (12) is provided between them.

4. The laser chip according to claim 1, characterized in that: Both the front and rear cavity surfaces of the chip are coated with anti-reflection films, and the reflectivity of the anti-reflection films is less than 1%. The chip is packaged in a butterfly package and contains a thermoelectric cooler and a thermistor.

5. The laser chip according to any one of claims 1 to 4, characterized in that: Prepared using the reconstructed equivalent chirp technique, including: Step 1, epitaxial growth: Using metal-organic chemical vapor deposition, a buffer layer (2), a lower cladding layer (3), a lower confinement layer (4), a multi-quantum well layer (5), an upper confinement layer (6), an electron blocking layer (7), a buffer layer (8), and a grating layer (9) are sequentially grown on a 2-inch n-type InP substrate. The active region is designed with a center wavelength of 1550 nm, the number of quantum wells is 5, and the material system is InGaAsP / InP. Step 2, fabrication of the sampling grating: Step 2.1: Coat photoresist on the grating layer (9), and define a uniform seed grating on the photoresist by holographic exposure, with a seed grating period of 240 nm; Step 2.2: Define the sampling structure using contact exposure, with a sampling period P of 4.244 μm; Step 3, secondary epitaxy and ridge waveguide etching: First, metal-organic chemical vapor deposition process is used to grow spacer layer (10), corrosion barrier layer (11), waveguide layer (12), lattice matching layer (12) and ohmic contact layer (14) in sequence; then, standard photolithography and inductively coupled plasma etching process is used to form ridge waveguide structure; Step 4, Electrical isolation and electrode fabrication: Step 4.1, for the ridge waveguide structure, between the two laser regions, the ohmic contact layer (14) and the lattice matching layer (13) are penetrated by ICP etching. Step 4.2, deposit Ti / Pt / Au metal electrodes on the ohmic contact layer (14) of the two laser regions by photolithography and lift-off process; Step 5, Cavity Surface Coating and Packaging: After chip cleaving, antireflection films are deposited on both the front and rear cavity surfaces. Finally, the chip is hermetically sealed in a butterfly package, housing a thermoelectric cooler and a thermistor.

6. A random number generation system, characterized in that: include: Chaotic laser: composed of a laser chip as described in any one of claims 1 to 5, used to generate chaotic light signals; DC bias drive circuit: used to provide DC bias current to the two laser regions; Optical coupling and transmission module: used for transmitting chaotic optical signals; Photoelectric detection module: used to receive chaotic light signals and linearly convert them into analog electrical signals; Data acquisition and post-processing module: Samples analog electrical signals and generates random numbers.

7. The random number generation system according to claim 6, characterized in that: An optical isolator is installed in the optical path to prevent reflected light from being fed back to the laser chip.

8. The random number generation system according to claim 6, characterized in that: Generate random numbers using the following method: The original chaotic data sequence X(t) is obtained by sampling the analog electrical signal; The difference data sequence Y(t) = X(t) - X(t-τ) is obtained through difference operation, where X(t-τ) is the data sequence after a delay time τ; A multi-bit extraction strategy is adopted to extract the lowest number of bits from each sampling point in Y(t) to form a random number bit stream.

9. The random number generation system according to claim 8, characterized in that: The analog electrical signal is continuously sampled with 8-bit quantization precision to form X(t), and the lowest 4 bits are extracted from each sampling point of Y(t) to form a random number bit stream.

10. The random number generation system according to claim 8, characterized in that: The delay time τ is selected as the time point where the autocorrelation function value of the sequence X(t) is the smallest and the cross-correlation coefficient is less than 0.

007. The delay time τ = 1 ns.

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