A broadband chaotic entropy source based on cross-injection of modulated semiconductor lasers

Abstract

This invention belongs to the field of chaotic communication technology, specifically relating to a broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers. It includes a first multimode chaotic laser module, an injection module, a second multimode chaotic laser module, and a photodetector. Its key feature is that: firstly, the chaotic semiconductor laser is directly modulated by optical feedback perturbation, causing the semiconductor laser to output a raw multimode chaotic laser signal. Then, using mutual injection perturbation, each longitudinal mode of the two raw multimode chaotic laser modules with different modulation frequencies undergoes beat frequency interaction. Furthermore, the detuning of the longitudinal mode undergoing beat frequency interaction gradually increases as it moves away from the center wavelength. Under the beat frequency interaction of multiple different detuning spectral modes, the output spectrum generated after photoelectric conversion is sequentially spliced ​​together, thereby achieving a significant increase in the bandwidth of the chaotic entropy source signal spectrum, theoretically reaching hundreds of GHz.

Description

Technical Field

[0001] This invention belongs to the field of chaotic communication technology, specifically, it relates to the generation of broadband chaotic laser based on mutual injection of modulated semiconductor lasers. Background Technology

[0002] Chaos is a type of noise-like signal with large-amplitude oscillations, and its output exhibits noise-like characteristics and a wide frequency spectrum. Compared to electronic technology for generating chaos, photonics technology makes it easier to generate broadband chaos and provides stronger anti-interference capabilities, thus leading to its wide range of applications. Examples include secure communication that uses chaos as a high-frequency carrier to modulate transmitted information and then recovers the information at the receiving end through chaotic synchronization; high-speed physical random number generation using chaos as a physical entropy source; and chaotic radar that uses chaotic lasers as a light source to detect and locate targets by correlating the signals reflected or scattered by the target with a reference waveform.

[0003] Semiconductor lasers belong to Class B lasers. By applying an external perturbation, such as optical feedback, optical injection, or photoelectric feedback, chaotic lasers can be easily generated. However, limited by the relaxation oscillation frequency, chaotic lasers generated through external perturbation have low bandwidth and uneven power spectra, severely restricting their applications. For example, the low chaotic bandwidth significantly reduces the transmission rate of chaotic-based secure communication, the generation rate of high-speed physical random numbers, and the detection range and resolution of chaotic lidar. Therefore, achieving the generation of high-bandwidth, spectrally flat chaotic laser sources is of significant research importance.

[0004] The mutual injection structure of semiconductor lasers is a typical method for generating broadband chaotic lasers. However, the spectral bandwidth of chaotic lasers generated by mutual injection is still limited, making it difficult to adapt to high-speed information transmission. To overcome these problems, this application proposes a method for generating ultra-wideband chaotic signals by directly modulating the driving current of a semiconductor laser using an external signal source, combined with a mutual injection perturbation structure. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a broadband chaotic entropy source structure based on the mutual injection of modulated semiconductor lasers to generate broadband chaotic signals with flat spectrum.

[0006] To achieve the above-mentioned objectives, the following technical measures can be adopted: a broadband chaotic entropy source based on the mutual injection of modulated semiconductor lasers is designed, characterized in that it includes: a first multimode chaotic laser module, an injection module, a second multimode chaotic laser module, and a photodetector.

[0007] The first multimode chaotic laser module consists of a first direct modulation signal, a first single-mode semiconductor laser, a first beam splitter, a first attenuator, and a first reflector. The first direct modulation signal is used to directly modulate the first single-mode semiconductor laser to generate multimode laser. The first beam splitter, the first attenuator, and the first reflector are used to form a feedback loop to perturb the optical field of the first single-mode semiconductor laser so that it outputs multimode chaotic laser.

[0008] The injection module consists of a polarization controller and a third attenuator. The polarization controller is used to adjust the polarization state of the output lasers of the first multimode chaotic laser module and the second multimode chaotic semiconductor laser module to achieve polarization state matching. The third attenuator is used to adjust the mutual injection optical power.

[0009] The second multimode chaotic laser module consists of a second direct modulation signal, a second single-mode semiconductor laser, a second beam splitter, a second attenuator, and a second reflector. The second direct modulation signal is used to directly modulate the second single-mode semiconductor laser to generate multimode laser. The second beam splitter, the second attenuator, and the second reflector form a feedback loop to perturb the optical field of the second single-mode semiconductor laser so that it outputs multimode chaotic laser.

[0010] The first single-mode semiconductor laser in the first multimode chaotic laser module is first directly modulated by a sinusoidal signal. After modulation, multiple modulation sidebands will be generated in the output laser spectrum to realize the generation of multi-longitudinal mode laser signals. Then, the output multi-longitudinal mode laser is split into two parts after passing through the first beam splitter. One part is reflected by the first mirror and returns to the first single-mode semiconductor laser to disturb its own optical field, thereby outputting the original multimode chaotic laser. The other part of the output chaotic laser then passes through the injection module composed of a polarization controller and a third attenuator, and is mutually injected and disturbed with the multimode chaotic laser output by the second multimode chaotic laser module after direct modulation and external cavity feedback. Finally, the second single-mode semiconductor laser outputs an ultra-wideband chaotic signal.

[0011] In this system, the direct modulation signal for each single-mode semiconductor laser is a sinusoidal or cosine current signal, which is controlled by the modulation frequency f. m and modulation depth m [m=I m / (I b -I th ), where I m For modulating current amplitude, I b For the bias current of the laser, I th[The threshold current of the laser] causes the output laser to generate upper and lower modulation sidebands. The increase in sidebands is manifested in the presence of multiple laser longitudinal modes in the spectrum. The modulation transforms the single-mode semiconductor laser into a multimode semiconductor laser with a mode spacing (equal to the modulation frequency) and controllable mode intensity (changing the modulation depth m of the modulation signal can increase the side mode energy).

[0012] Among them, the controllable multimode laser output by the current-modulated single-mode semiconductor laser outputs the original multimode chaotic laser under the action of optical feedback. The spectral and spectral characteristics of the chaotic laser can be controlled by adjusting the attenuator to change the feedback intensity k.

[0013] Among them, the two original multimode chaotic laser signals output by the first multimode chaotic laser module and the second multimode chaotic laser module are mutually injected and disturbed. After mutual injection, the corresponding modes of the first multimode chaotic laser module and the second multimode chaotic laser module will generate a beat frequency effect, forming a disturbance structure of multiple single-mode optical feedback combined with mutual injection.

[0014] In this process, the modulation frequencies of the direct modulation signals applied by the first multimode chaotic laser module and the second multimode chaotic laser module should be different. After modulation, the frequency detuning of the first multimode chaotic laser module and the second multimode chaotic laser module in the mutual injection perturbation structure gradually increases as the center wavelength moves further away. Multiple spectral modes with different frequency detunings are perturbed by the mutual injection structure. Each mode output by the second multimode chaotic laser module after injection perturbation will excite a new oscillation mode near it, and the frequency detuning of each new oscillation mode with the original mode will gradually increase. After passing through the photoelectric converter, the broadband chaotic signal spliced ​​by the spectrum of the second multimode chaotic laser module is finally output.

[0015] In this process, changing the modulation frequency and modulation depth of the first single-mode semiconductor laser and the second single-mode semiconductor laser can change the number of modes and mode intensity of the modulated multimode laser, and thus change the number and width of the spectral "segmentation" after mutual injection, thereby achieving the adjustment of the bandwidth and flatness of the final chaotic signal spectrum.

[0016] Specifically, by adjusting the frequency detuning and injection intensity between the mutual injection structures, the bandwidth and flatness of the output chaos are ultimately changed.

[0017] Compared with existing technologies, the implementation steps and advantages of the broadband chaotic entropy source based on direct modulation of semiconductor lasers in this invention are as follows:

[0018] 1. This invention utilizes a sine or cosine signal to directly modulate two chaotic single-mode semiconductor lasers. After modulation, the output spectrum of the lasers will exhibit modulation sidebands, achieving multi-longitudinal-mode chaotic output. Furthermore, the mode spacing, mode intensity, and number of modes between the longitudinal modes can be adjusted by regulating the modulation frequency f of the sine signal.m The output characteristics of multi-mode lasers can be easily realized and adjusted by changing the laser mode interval (equal to the modulation frequency) and modulation depth m.

[0019] 2. By perturbing the generated multimode laser through optical feedback and adjusting the attenuator to change the feedback intensity k, the modulated laser outputs a multimode chaotic state. The spectral linewidth of the multimode chaotic laser generated by optical feedback will be broadened, and the frequency characteristics of the output signal will be complex.

[0020] 3. Under the mutual injection perturbation of the first multimode chaotic laser module and the second multimode chaotic laser module, each longitudinal mode in the spectrally broadened multimode chaotic laser beats with the corresponding longitudinal mode from the other laser. The frequency detuning of each longitudinal mode is different. After photoelectric conversion, the output spectrum of different frequency components will be spliced ​​together, which greatly improves its bandwidth and enhances its flatness.

[0021] In this invention, the output chaotic laser bandwidth depends on the modulation signals (modulation depth m and modulation frequency f) applied to the first and second single-mode semiconductor lasers. m The parameters include the feedback intensity, frequency detuning between the two lasers, and injection intensity. Therefore, the chaos output by this scheme not only has a high bandwidth and is easy to control, but also has adjustable spectral bandwidth and flatness. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers provided by the present invention. Wherein, DM1, DM2: first direct modulation signal, first direct modulation signal; SL1, SL2: first single-mode semiconductor laser, second single-mode semiconductor laser; FC1, FC2: first beam splitter, second beam splitter; M1, M2: first reflector, second reflector; VOA1, VOA2, VOA3: ​​first attenuator, second attenuator, third attenuator; PC: polarization controller; PD: photodetector. Solid lines represent optical paths, and dashed lines represent circuits.

[0023] Figure 2 The present invention provides a schematic diagram of the spectrum and spectral characteristics of a broadband chaotic entropy source based on the mutual injection of modulated semiconductor lasers. Detailed Implementation

[0024] To achieve the above-mentioned objectives, the following technical measures can be adopted: a broadband chaotic entropy source based on the mutual injection of modulated semiconductor lasers is designed, characterized in that it includes: a first multimode chaotic laser module, an injection module, a second multimode chaotic laser module, and a photodetector.

[0025] The first multimode chaotic laser module consists of a first direct modulation signal (DM1), a first single-mode semiconductor laser (SL1), a first beam splitter (FC1), a first attenuator (VOA1), and a first reflector (M1). The first direct modulation signal (DM1) is used for direct modulation of the first single-mode semiconductor laser (SL1), and the first beam splitter (FC1), the first attenuator (VOA1), and the first reflector (M1) are used to form a feedback loop to perturb the field of the first single-mode semiconductor laser (SL1) so that it outputs multimode chaotic laser.

[0026] The injection module consists of a polarization controller (PC) and a third attenuator (VOA3). The polarization controller (PC) is used to adjust the polarization state of the output lasers of the first multimode chaotic laser module and the second multimode chaotic semiconductor laser module to achieve polarization state matching. The third attenuator (VOA3) is used to adjust the mutual injection optical power.

[0027] The second multimode chaotic laser module consists of a second direct modulation signal (DM2), a second single-mode semiconductor laser (SL2), a second beam splitter (FC2), a second attenuator (VOA2), and a second reflector (M2). The second direct modulation signal (DM2) is used for direct modulation of the second single-mode semiconductor laser (SL2). The second beam splitter (FC2), the second attenuator (VOA2), and the second reflector (M2) are used to form a feedback loop to perturb the field of the second single-mode semiconductor laser (SL2) so that it outputs multimode chaotic laser.

[0028] In the multimode chaotic laser module, the spectrum of the laser signal output from the single-mode semiconductor laser after direct current signal modulation will generate modulation sidebands, forming a multi-longitudinal-mode laser with controllable mode spacing. (See [reference needed]). Figure 2 (a1) Spectrum diagram. The gray line represents the spectrum of the first single-mode semiconductor laser (SL1) after direct modulation (modulation frequency of 8.6 GHz), with an interval of 8.6 GHz between each mode. The black line represents the spectrum of the second single-mode semiconductor laser (SL2) after direct modulation (modulation frequency of 7.8 GHz), with an interval of 7.8 GHz between each mode. The modulation frequency difference between the first single-mode semiconductor laser (SL1) and the second single-mode semiconductor laser (SL2) is 0.8 GHz, so the mode spacing difference of the resulting multimode laser is 0.8 GHz. Figure 2(b1) shows the spectrum of the corresponding directly modulated single-mode semiconductor laser. The gray line represents the spectrum of the first single-mode semiconductor laser (SL1) after modulation, and the black line represents the spectrum of the second single-mode semiconductor laser (SL2) after modulation. The multi-longitudinal-mode laser output from the first single-mode semiconductor laser is split into two parts by the first beam splitter (FC1): one part is reflected by the first mirror (M1) and returns to the single-mode semiconductor laser to perturb its own optical field. Adjusting the first attenuator (VOA1) to make the feedback intensity 0.25 allows for the output of a linewidth-enhanced original multi-mode chaotic laser. The structure of the second multi-mode chaotic laser module is similar to that of the first multi-mode chaotic laser module. After modulation and optical feedback (feedback intensity of 0.25), it generates a mode-based original multi-mode chaotic laser. Figure 2 (a2) shows the spectral linewidth broadening of the directly modulated second single-mode semiconductor laser after optical feedback. The spectrum shows that due to optical feedback, the frequency components in the spectrum increase significantly, the linewidth broadens, and the output of the single-mode semiconductor laser changes from a modulated single-cycle state to a chaotic state. Furthermore, corresponding modulation peaks can be observed at the corresponding modulation frequencies, such as... Figure 2 (b2). The two original multimode chaotic lasers output from the first and second multimode chaotic laser modules are mutually injected and perturbed by an injection module consisting of a polarization controller (PC) and a third attenuator (VOA3). The frequency detuning of the center wavelength is adjusted to 80 GHz and the injection intensity to 1.5. After beat frequency and photoelectric conversion for each corresponding mode, a broadband enhanced chaotic signal is finally output from one end of the second multimode chaotic laser module. The spectrum and frequency spectrum of the final output chaotic signal are as follows: Figure 2 (d1) and Figure 2 As shown in (d2), the calculated spectral -10dB linewidth of the generated chaotic signal is 149 GHz, the 80% bandwidth of the spectrum is 61.1 GHz, and the low-frequency energy is raised, resulting in a flat spectrum with a flatness of 0.85. Compared to the spectrum (-10dB linewidth of 89 GHz) and spectrum (bandwidth of 29.7 GHz) generated by mutual injection of two single-mode semiconductor lasers, the linewidth increases by 1.67 times, and the bandwidth increases by approximately 2.1 times.

[0029] Compared with existing technologies, the advantages of this invention based on the broadband chaotic entropy source of direct modulation semiconductor laser mutual injection are as follows:

[0030] 1. This invention utilizes optical feedback results, mutual injection structure and direct modulation technology to generate broadband chaotic signals, resulting in a more flat spectrum and more complex frequency characteristics of the generated chaotic signals;

[0031] 2. The chaotic signal output characteristics described in this invention depend on the feedback parameters (feedback strength), mutual injection parameters (frequency detuning and injection strength), and modulation parameters (modulation depth m and modulation frequency f). m Therefore, the spectral characteristics of the output chaotic signal can be adjusted and customized according to requirements;

[0032] 3. The broadband chaotic signal generated by this invention is composed of multiple spectra generated by beating different frequency components in a multimode chaotic laser. Therefore, theoretically, it is possible to generate a chaotic signal with a spectral bandwidth of hundreds of GHz.

[0033] For researchers and technicians engaged in the field of this invention, the above-described embodiments are merely one specific implementation method of this invention, and this method does not limit the scope of protection of this invention. The relevant limitations in the technical specification and its appendices of this invention, applied directly or indirectly to other related scientific and technological fields in various equivalent forms or methods, also fall within the scope of patent protection of this invention.

Claims

1. A broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers, characterized in that, include: The system comprises a first multimode chaotic laser module, an injection module, a second multimode chaotic laser module, and a photodetector. The first multimode chaotic laser module consists of a first direct modulation signal, a first single-mode semiconductor laser, a first beam splitter, a first attenuator, and a first reflector. The injection module consists of a polarization controller and a third attenuator. The second multimode chaotic laser module consists of a second direct modulation signal, a second single-mode semiconductor laser, a second beam splitter, a second attenuator, and a second reflector. The direct modulation signal is used to directly modulate the single-mode semiconductor laser to generate a multimode laser. The beam splitter, attenuator, and reflector form a feedback loop to perturb the optical field of the multimode laser, causing it to output a multimode chaotic laser. The first multimode chaotic laser module, after direct modulation and external cavity feedback... The chaotic laser module and the second multimode chaotic laser module, which is directly modulated and has external cavity feedback, mutually inject and perturb each other. Each mode output by the second multimode chaotic laser module after injection and perturbation will generate a new oscillation mode near it, and the frequency detuning between each new oscillation mode and the original mode will gradually increase. After passing through the photoelectric converter, the broadband chaotic signal spliced ​​by the output spectrum of the second multimode chaotic laser module is finally generated. The two original multimode chaotic laser signals output by the first multimode chaotic laser module and the second multimode chaotic laser module mutually inject and perturb each other. After mutual injection, the corresponding modes of the first multimode chaotic laser module and the second multimode chaotic laser module will generate a beat frequency effect, forming a perturbation structure of multiple single-mode optical feedback combined with mutual injection.

2. The broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers as described in claim 1, characterized in that: Each single-mode semiconductor laser can be directly modulated by a sine or cosine electrical signal, by adjusting the modulation frequency f of the modulation signal. m The modulation depth m can be used to adjust the mode spacing and mode intensity of the multimode chaotic laser, where the mode spacing is equal to the direct modulation frequency and the mode intensity depends on the modulation depth.

3. The broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers as described in claim 1, characterized in that: The modulation frequencies of the direct modulation signals applied to the first multimode chaotic laser module and the second multimode chaotic laser module should be different. After modulation, the frequency detuning of the corresponding modes of the first and second multimode chaotic laser modules in the mutual injection perturbation structure gradually increases as the center wavelength moves away. After the spectral modes with different frequency detunings are perturbed by the mutual injection structure, the spectra of the chaotic laser generated after conversion by the photodetector will be spliced ​​together to finally output a broadband enhanced chaotic signal.

4. A broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers as described in claim 3, characterized in that: By changing the modulation frequency and modulation depth of the first and second single-mode semiconductor lasers, the number and intensity of the modulated multimode laser can be altered. This, in turn, can change the number and width of the spectral "segments" after mutual injection, thereby adjusting the bandwidth and flatness of the final chaotic signal spectrum.

5. A broadband chaotic entropy source based on mutual injection of modulated semiconductor lasers as described in claim 3, characterized in that: By adjusting the frequency detuning and injection intensity between the mutual injection structures, the bandwidth and flatness of the output chaos are ultimately changed.

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