劉勁楊,周雪芳*,畢美華,楊國偉,王天樞
光混沌保密通信系統(tǒng)在MATLAB與OptiSystem中的協(xié)同實(shí)現(xiàn)
劉勁楊1,周雪芳1*,畢美華1,楊國偉1,王天樞2
1杭州電子科技大學(xué)通信工程學(xué)院,浙江 杭州 310018;2長春理工大學(xué)空間光電技術(shù)國家地方聯(lián)合工程研究中心,吉林 長春 130022
基于兩個(gè)具有平行結(jié)構(gòu)的電光時(shí)延反饋環(huán),本文設(shè)計(jì)了一種電光強(qiáng)度混沌通信系統(tǒng)。通過混沌注入混沌的方式來產(chǎn)生更加復(fù)雜的混沌波形,增強(qiáng)混沌復(fù)雜程度以及通信系統(tǒng)的保密性。在本次設(shè)計(jì)中,采用MATLAB與OptiSystem協(xié)同的方式來對(duì)該系統(tǒng)進(jìn)行仿真,解決了OptiSystem不能模擬光學(xué)反饋環(huán)路的問題。由OptiSystem中成熟的激光器和二進(jìn)制序列生成模塊為系統(tǒng)提供能量與輸入信號(hào),由MATLAB程序?qū)崿F(xiàn)電光時(shí)延反饋環(huán),并在OptiSystem中完成信號(hào)在光纖鏈路中的傳輸。文章介紹了如何利用MATLAB與OptiSystem實(shí)現(xiàn)混沌系統(tǒng)的協(xié)同仿真,并通過數(shù)值模擬表明,提出的用于模擬光學(xué)反饋環(huán)路的方法具有可行性,設(shè)計(jì)的混沌系統(tǒng)的性能與理論值吻合,證明了該混沌生成方式的可行性。
混沌;混沌加密;電光時(shí)延;MATLAB;OptiSystem
隨著對(duì)通信容量、速度以及保密性等需求的增加,光纖通信已經(jīng)成為信息傳遞的重要方式,但在傳輸?shù)倪^程中,存在著被非法接收者竊聽的風(fēng)險(xiǎn),所以對(duì)光纖中傳輸?shù)男盘?hào)進(jìn)行加密是十分必要的?;煦绫C芡ㄐ攀腔诨煦缧盘?hào)的物理層硬件加密,憑借著混沌信號(hào)所具有的非周期、連續(xù)寬帶頻譜、類噪聲和不可長期預(yù)測等優(yōu)勢[1],將信息隱藏在混沌信號(hào)中傳輸,并在接收端通過與發(fā)射端同步的混沌波形解調(diào)出所傳輸?shù)男畔?,在保密通信領(lǐng)域有著極大的應(yīng)用前景,引起國內(nèi)外研究人員的廣泛關(guān)注。
1960年Maiman發(fā)明了激光器,1963年氣象學(xué)家Lorenz首次提出混沌的概念,直至1990年P(guān)ecora和Carroll提出并驗(yàn)證了混沌同步,從此結(jié)束了混沌與激光獨(dú)立發(fā)展的時(shí)代,開啟了通信領(lǐng)域的新紀(jì)元。
傳統(tǒng)的電混沌信號(hào)存在帶寬窄、信息傳輸速率低的問題而無法滿足現(xiàn)代通信的需求[2]。1998年,Van Wiggeren和Roy用光纖激光器實(shí)驗(yàn)演示了10 MHz的背靠背混沌通信系統(tǒng)。2005年,Syvridis等[3]人在120 km的商用光纖網(wǎng)絡(luò)中成功實(shí)現(xiàn)了可以單向傳輸信息的混沌保密通信系統(tǒng),混沌光保密通信系統(tǒng)不僅具有實(shí)現(xiàn)非線性延遲動(dòng)力學(xué)系統(tǒng)的固有能力,并且提供高復(fù)雜性和無限維混沌動(dòng)力[4]。隨后,各國科學(xué)家不斷致力于提高混沌通信的傳輸速率、信號(hào)質(zhì)量以及安全性能[5]。2020年,研究人員成功實(shí)現(xiàn)了10 Gb/s相位調(diào)制信號(hào)的傳輸[6],傳輸距離高達(dá)1000 km,證明了長距離、高速混沌保密通信的可行性,并采用相位混沌加密的方式進(jìn)一步提高了信號(hào)傳輸?shù)陌踩?。這是因?yàn)橄啾扔趶?qiáng)度混沌,相位混沌具有恒定的振幅,進(jìn)一步提高了混沌的復(fù)雜程度,增加了第三方的破解難度。因此,尋找復(fù)雜度更高的混沌產(chǎn)生方案對(duì)混沌保密通信而言意義重大。
混沌信號(hào)的產(chǎn)生離不開光學(xué)器件的非線性動(dòng)力學(xué)特性,如半導(dǎo)體激光器、馬赫-曾德爾調(diào)制器、馬赫-曾德爾干涉儀等。其中較為常見的是利用馬赫-曾德爾調(diào)制器的電光時(shí)延反饋環(huán),能夠提供足夠的非線性效應(yīng)產(chǎn)生混沌信號(hào)。針對(duì)混沌保密通信中的安全性問題,本文結(jié)合兩個(gè)具有平行結(jié)構(gòu)的電光時(shí)延反饋環(huán),提出了一種可以產(chǎn)生復(fù)雜混沌波形的電光強(qiáng)度混沌系統(tǒng)。該混沌通信系統(tǒng)創(chuàng)新性地借助MATLAB與OptiSystem協(xié)同仿真實(shí)現(xiàn)。其中,OptiSystem軟件是加拿大OptiWave公司開發(fā)的一套光通信系統(tǒng)設(shè)計(jì)軟件和仿真軟件,但由于OptiSystem軟件是按單向、順序流程執(zhí)行算法和仿真過程[7],無法支持循環(huán)反饋流程,因而無法獨(dú)立模擬帶有反饋環(huán)路的結(jié)構(gòu)。而具有強(qiáng)大數(shù)值處理功能的MATLAB恰巧可以通過循環(huán)和迭代賦值語句來模擬光反饋環(huán)路的信號(hào)處理過程。利用MATLAB輔助OptiSystem可以順利實(shí)現(xiàn)電光時(shí)延反饋環(huán)的模擬,成功搭建混沌保密通信系統(tǒng)。本文通過仿真驗(yàn)證了該混沌生成方案下延遲混沌動(dòng)力的同步性,和同步的魯棒性,研究了不同傳輸距離下發(fā)射端與接收端的同步程度,證明了該混沌生成方案的可行性。
具有兩個(gè)電光時(shí)延反饋環(huán)的強(qiáng)度混沌裝置如圖1所示。發(fā)射端與接收端都由兩個(gè)電光時(shí)延反饋環(huán)組成,下標(biāo)=1、2代表兩個(gè)不同的反饋環(huán)(=1對(duì)應(yīng)外反饋環(huán),=2對(duì)應(yīng)內(nèi)反饋環(huán))。馬赫-曾德爾調(diào)制器(Mach-Zehnder modulator,MZM1)將1()調(diào)制到由半導(dǎo)體激光器(semiconductor laser,SL1)產(chǎn)生的載波上,它的輸出經(jīng)過50/50耦合器(optical coupler,OC)分為兩部分,一部分輸入信道中,另一部分注入由2()進(jìn)行調(diào)制的MZM2中。雙強(qiáng)度調(diào)制后的信號(hào)由延遲線(delay line,DL2)整體延遲2的時(shí)間,然后分為兩路各自注入內(nèi)外反饋環(huán)中,注入內(nèi)反饋環(huán)的信號(hào)由光電二極管(PD)轉(zhuǎn)化為電波,并放大為MZM2的驅(qū)動(dòng)信號(hào),形成反饋回路。另一路信號(hào)輸入延遲時(shí)間為1的光纖線路中,轉(zhuǎn)化為MZM1的輸入。需要注意的是,只有MZM1的輸出進(jìn)入信道中傳輸,MZM2的輸出被隱藏在發(fā)射端內(nèi)部,兩個(gè)電光時(shí)延反饋環(huán)的設(shè)置增強(qiáng)了輸出混沌的復(fù)雜程度。在傳輸信道中,采用色散補(bǔ)償光纖(dispersion compensation fiber,DCF)對(duì)信道損傷進(jìn)行簡單補(bǔ)償。接收端與發(fā)射端采用相同的參數(shù),信道傳來的混沌信號(hào)經(jīng)過OC分為兩部分,一部分驅(qū)動(dòng)接收端與發(fā)射端同步,并由PD轉(zhuǎn)化為電信號(hào),另一路直接完成光電轉(zhuǎn)換,兩路相減即可恢復(fù)出二進(jìn)制序列。
圖1 具有兩個(gè)電光時(shí)延反饋環(huán)的強(qiáng)度混沌裝置圖
OptiSystem軟件按單向、順序流程執(zhí)行仿真過程,該處理方式使得后級(jí)器件的輸出信號(hào)反饋回前級(jí)器件時(shí)無法觸發(fā)新的仿真運(yùn)算,因此考慮MATLAB輔助OptiSystem實(shí)現(xiàn)反饋環(huán)路,MATLAB與OptiSystem協(xié)同仿真實(shí)現(xiàn)思路如圖2 (以發(fā)射端為例)。
綜上,生成的協(xié)同仿真實(shí)驗(yàn)圖如圖3所示。
圖2 協(xié)同仿真實(shí)現(xiàn)思路流程圖
表1 發(fā)射端MATLAB元件端口參數(shù)
表2 MATLAB元件Main菜單設(shè)置
圖3 MATLAB與OptiSystem協(xié)同仿真具有兩個(gè)電光時(shí)延反饋環(huán)的強(qiáng)度混沌裝置圖
無信息搭載時(shí),MATLAB與OptiSystem協(xié)同仿真產(chǎn)生的混沌序列及其放大圖如圖4(a)、4(b)所示,高低脈沖振幅互相跟隨[13],并利用自相關(guān)函數(shù)評(píng)估該序列的隨機(jī)性,對(duì)于混沌序列(),自相關(guān)函數(shù)(ACF,用ACF表示)可被定義為
其中:<…>表示時(shí)間平均值。由圖4(c)可以看出,該序列僅在延遲時(shí)間為0時(shí)具有較強(qiáng)的相關(guān)性,其余時(shí)間相關(guān)程度十分低,證明該混沌脈沖具有幅度隨機(jī)性,可有效起到隱蔽信息、提高通信安全性的作用。
同樣在無信息搭載的情況下,分析該系統(tǒng)的同步性及魯棒性[14],選取任意時(shí)間段(310 ns~320 ns)內(nèi)發(fā)射
端與接收端的混沌序列,如圖5所示,可發(fā)現(xiàn)該時(shí)間段內(nèi)所有時(shí)刻,發(fā)射端與接收端的混沌波形具有相同的趨勢,并對(duì)所有時(shí)間段的混沌波形進(jìn)行同步性驗(yàn)證。如圖6所示,橫坐標(biāo)為發(fā)射端的混沌強(qiáng)度,縱坐標(biāo)為接收端的混沌強(qiáng)度,兩者完全擬合于=這條曲線,證明了發(fā)射端與接收端波形的同步現(xiàn)象是普遍存在的,而非某一時(shí)間段內(nèi)的特殊現(xiàn)象,即該混沌通信系統(tǒng)具有同步性。
圖4 MATLAB與OptiSystem協(xié)同仿真產(chǎn)生的混沌波形。(a) 混沌波形圖;(b) 混沌波形放大圖;(c) 混沌波形的自相關(guān)性
隨后,向SL2引入一個(gè)方波擾動(dòng),調(diào)制后的方波耦合到MZM1,使發(fā)射端反饋強(qiáng)度發(fā)生變化,發(fā)射端與接收端的時(shí)間序列分別如圖7(a)、7(b)所示。發(fā)射端于=200 ns時(shí)引入一個(gè)15 ns的擾動(dòng);在引入擾動(dòng)前,兩端處于完全同步狀態(tài),差值恒為0;直至200 ns,接收端出現(xiàn)與發(fā)射端同步的擾動(dòng)并在15 ns后結(jié)束。結(jié)果說明在引入外部擾動(dòng)的情況下,延遲混沌動(dòng)力學(xué)的同步解仍能夠保持,并沒有因?yàn)橐霐_動(dòng)而永久喪失同步性能,證明該混沌通信系統(tǒng)具有一定的自我修復(fù)、抗干擾能力,即魯棒性。
上述仿真實(shí)驗(yàn)說明,在發(fā)射端與接收端所有參數(shù)都匹配的條件下,兩端產(chǎn)生的混沌序列具有同步性并能夠抵抗一定的外部擾動(dòng),因此可利用該系統(tǒng)進(jìn)行信息的加解密傳輸。
采用OptiSystem中的二進(jìn)制序列生成器生成序列000000111000111111000111111000,并將該信息耦合到電光時(shí)延反饋環(huán)中,經(jīng)兩次強(qiáng)度調(diào)制后,送入信道中進(jìn)行傳輸,發(fā)射端已搭載信息的混沌序列如圖8(a)所示,傳輸距離為1 km,并采用0.2 km的DCF補(bǔ)償線性損傷,接收端恢復(fù)出的信息序列如圖8(c)所示,與輸入的信息完全吻合。圖8(d)是兩端混沌強(qiáng)度的散點(diǎn)圖,由于傳輸過程中的衰減與損耗,各點(diǎn)并不完全擬合于=,而是分布在=兩側(cè),由于發(fā)射端混沌搭載了信息序列,所以在曲線附近呈非均勻分布狀態(tài)[15],但仍能體現(xiàn)發(fā)射端與接收端的同步性。
圖5 某段時(shí)間內(nèi),發(fā)射端與接收端的波形功率對(duì)比圖
圖6 發(fā)射端與接收端的混沌強(qiáng)度擬合圖
圖7 系統(tǒng)魯棒性研究。(a) 發(fā)射端引入的擾動(dòng);(b) 接收端的同步誤差
圖8 (a) 發(fā)射端混沌波形;(b) 接收端混沌波形;(c) 恢復(fù)出的信息;(d) 發(fā)射端與接收端混沌強(qiáng)度散點(diǎn)圖
由上述仿真結(jié)果可知,發(fā)射端與接收端混沌的同步程度是能否有效進(jìn)行加解密操作的決定因素,為評(píng)估系統(tǒng)的同步性,這里引入歸一化互相關(guān)函數(shù)來測評(píng)發(fā)射端與接收端之間的同步程度,歸一化互相關(guān)函數(shù)[16]定義為
其中:1()與1()對(duì)應(yīng)圖1中的發(fā)射端混沌與接收端混沌,<…>表示平均值。
圖9反映的是不同補(bǔ)償情況下,傳輸距離與互相關(guān)函數(shù)之間的關(guān)系,此處不考慮對(duì)衰減的補(bǔ)償。隨著傳輸距離的增加,系統(tǒng)的同步性大幅下降。隨后增加色散補(bǔ)償光纖對(duì)色散進(jìn)行補(bǔ)償,在相同距離下,有效提高了系統(tǒng)的同步程度及加解密信息的質(zhì)量[17]。
圖9 不同補(bǔ)償情況下,傳輸距離與互相關(guān)函數(shù)之間的關(guān)系
本文使用MATLAB輔助OptiSystem實(shí)現(xiàn)光學(xué)反饋環(huán)路的模擬,將MATLAB的數(shù)值計(jì)算能力與OptiSystem的仿真模擬能力相結(jié)合,成功搭建具有兩個(gè)電光時(shí)延反饋環(huán)的強(qiáng)度混沌裝置,仿真結(jié)果與理論值相吻合,生成的混沌序列具有同步性及魯棒性,可有效對(duì)信息進(jìn)行加解密操作,為后續(xù)混沌生成方案的研究提供了思路。除此之外,實(shí)現(xiàn)MATLAB與OptiSystem的協(xié)同仿真,可按照使用者意愿設(shè)計(jì)虛擬器件,對(duì)新型光電器件的研究和開發(fā)具有重要意義。
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Co-simulation of optical chaotic secure communication systems in MATLAB and OptiSystem
Liu Jinyang1, Zhou Xuefang1*, Bi Meihua1, Yang Guowei1, Wang Tianshu2
1School of Communication Engineering, Hangzhou Dianzi University, Hangzhou, Zhejiang 310018, China;2National and Local Joint Engineering Research Center of Space Optoelectronics Technology, Changchun University of Science and Technology, Changchun, Jilin 130022, China
Zoomed figure of chaotic wave
Overview:With the increase in demand for communication capacity, speed, and confidentiality, optical fiber communication has become an important way of information transmission. However, during the transmission process, there is a risk of being eavesdropped on by illegal receivers. Therefore, it is very necessary to encrypt the signal transmitted in optical fibers. Chaotic secure communication is the physical hardware encryption based on chaotic signals. With the chaotic signal has the advantages of aperiodic, continuous broadband spectrum, noise-like, and unpredictable long-term, information is hidden in chaotic signals for transmission, and the transmitted information is demodulated by the chaotic waveform synchronized with the transmitter at the receiver. Chaotic secure communication has a great application prospect in the secure communication field and has attracted extensive attention from researchers at home and abroad.
Based on two parallel electro-optic delay feedback loops, an electro-optic intensity chaotic system is designed in this paper. By injecting chaos into chaos, more complex chaotic waveforms can be generated to enhance the chaotic complexity and the communication system confidentiality. In this design, MATLAB and OptiSystem are used to simulate the system, which solves the difficulty that OptiSystem could not simulate the optical feedback loop. Combining MATLAB’s numerical calculation capabilities with OptiSystem’s simulation capabilities, an intensity chaotic device with two electro-optic delay feedback loops has been successfully constructed. The mature laser and binary sequence generation modules in OptiSystem provide energy and input signals to the system. The electro-optic delay feedback loop is realized by the MATLAB program, and the signal transmission in the optical fiber link is completed in OptiSystem. The simulation results show that the generated chaotic sequence has amplitude randomness, and the high and low pulse amplitudes follow each other, which can effectively conceal information. The chaotic sequence at the transmitter and receiver has synchronization and robustness. In the case of no information loading, the chaotic sequence intensity at both ends completely fits=. When an external disturbance is introduced, the synchronization solution of the delayed chaotic dynamics at both ends can still be maintained well and it has a certain anti-interference ability. These properties ensure that the system could be used for information encryption operation effectively, and the relationships between the transmission distance and the chaos synchronization at both ends under different compensation situations have been studied. The simulation results are in good agreement with the theoretical values, which proves the feasibility of the chaotic generation method and provides ideas for the subsequent research and simulation on chaotic generation schemes.
Liu J Y, Zhou X F, Bi M H,Co-simulation of optical chaotic secure communication systems in MATLAB and OptiSystem[J]., 2021, 48(9): 210146; DOI:10.12086/oee.2021.210146
Co-simulation of optical chaotic secure communication systems in MATLAB and OptiSystem
Liu Jinyang1, Zhou Xuefang1*, Bi Meihua1, Yang Guowei1, Wang Tianshu2
1School of Communication Engineering, Hangzhou Dianzi University, Hangzhou, Zhejiang 310018, China;2National and Local Joint Engineering Research Center of Space Optoelectronics Technology, Changchun University of Science and Technology, Changchun, Jilin 130022, China
An electro-optic intensity chaotic communication system is designed by combining two electro-optic delay feedback loops with parallel structures. By injecting chaos into chaos, a more complex chaotic waveform is generated to enhance the chaotic complexity and the communication system confidentiality. In this design, MATLAB and OptiSystem software are used to simulate the system, which solves the problem that OptiSystem software can't simulate the optical feedback loop. The mature laser and binary sequence generation modules in OptiSystem software provide energy and input signals for the system. The electro-optic delay feedback loops are realized by the MATLAB program, and the signal transmission in optical fibers is completed in the OptiSystem software. The article introduces how to use MATLAB and OptiSystem software to realize the co-simulation of chaotic systems. Numerical simulations show that the proposed method is feasible to simulate the optical feedback loop, and the simulation results are in good agreement with the theoretical values, which prove that the chaotic signal is generated.
chaos; chaotic encryption; electro-optic delay; MATLAB; OptiSystem
劉勁楊,周雪芳,畢美華,等. 光混沌保密通信系統(tǒng)在MATLAB與OptiSystem中的協(xié)同實(shí)現(xiàn)[J]. 光電工程,2021,48(9): 210146
Liu J Y, Zhou X F, Bi M H,Co-simulation of optical chaotic secure communication systems in MATLAB and OptiSystem[J]., 2021, 48(9): 210146
436
A
10.12086/oee.2021.210146
2021-05-06;
2021-08-16
國家自然科學(xué)基金資助項(xiàng)目(61705055);浙江省重點(diǎn)研發(fā)計(jì)劃資助項(xiàng)目(2019C01G1121168)
劉勁楊(1998-),女,碩士研究生,主要從事激光混沌保密通信系統(tǒng)的研究。E-mail:905995272@qq.com
周雪芳(1976-),女,博士生導(dǎo)師,副教授,主要從事光纖激光器、光纖傳感技術(shù)和智能天線技術(shù)的研究。E-mail:zhouxf@hdu.edu.cn
National Natural Science Foundation of China (61705055) and Zhejiang Provincial Key Research and Development Program (2019C01G1121168)
* E-mail: zhouxf@hdu.edu.cn