Experimental Investigation of Improving the Performance of the Chaotic Optical Communication with Chaos-Masking through Wavelength Mismatch

doi:10.4236/opj.2013.32B044

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Optics and Photonics Journal, 2013, 3, 183-186

doi:10.4236/opj.2013.32B044 Published Online June 2013 (http://www.scirp.org/journal/opj)

Experimental Investigation of Improving the Performance

of the Chaotic Optical Communication with

Chaos-Masking through Wavelength Mismatch*

Wei Chang, Xiaolei Chen, Qingchun Zhao, Hongxi Yin, Nan Zhao

Lab of Optical Communications and Photonic Technology, School of Information and Communication Engineering,

Dalian University of Technology, Dalian, China

Email: [email protected]

Received 2013

ABSTRACT

In this paper, the wavelength mismatch between the message and the chaotic carrier in the chaotic optical communica-

tion with c hao s-ma ski ng ha s b een e xpe ri mental ly i nve stiga te d. T he result s sho w t hat the d ec ryptio n p erfo rma nce o f t he

receiver can be improved when the message wavelength is greater than that of the chaotic carrier. When the wavelength

offset i s set to 0.12 nm, high-speed secure optical communication with a message of 2.5 Gbits/s is achieved.

Keywords: Chaos Masking; Chaotic Synchronization; Chaotic Communication; Wavelength Mismatch

1. Introduction

As a hardware-based encryption technique at the physical

layer, the chaotic optical communication has attracted

extensive interests from the community of secure and

optical communications during the past decade [1,2]. At

the receiver, the message can be filtered out by the re-

ceiver laser, and the chaotic carrier that synchronizes

with the carrier generated by the transmitter can be ob-

tained. Then, the message can be decrypted by subtract-

ing the output of the receiver laser from the encrypted

signal [3 ,4] . With the in-depth exploring the secure chao-

tic optical communication, the issues for secure chaotic

optical communication mainly focus on bandwidth en-

hancement [5], generation of novel chaotic carriers [6],

chaotic photonic integrated circuits (PICs) [7], and bidi-

rectional communications [8]. It is important to solve

these issues for which can improve the performance of

the system and promote the practical applications. How-

ever, the encryption schemes as well as the relationship

between the message and the chaotic carrier is the most

important factor, which constraints the performance of

the secure chaotic optical communication system direct-

ly.

At present, three encryption schemes have been pro-

posed for the secure chaotic optical communications,

name ly, chaos modulation (CM), chaos masking (CMS),

and chaos shift-keying (CSK) [9]. For simple physical

processes and convenient achievement, CMS is the most

common encryption scheme. Argyris et al. experimen-

tally investigated the performance of the three encryption

schemes with a message of 1.5 Gbits/s [10]. However, it

is still a problem being worthy further investigating how

to improve the performance of different encryption

schemes and to promote the data-rate of message.

In this p aper , the misma tch o f the wavel engt h between

the message and the chaotic carrier in the secure chaos-

masking optical communication has been experimentally

investigated. The relationship between the mismatch of

the wavelength and the performance of the system has

been quantitatively analyzed. When the wavelength off-

set is set to 0.12 nm, high-speed secure communication

with a message of 2.5 Gbits/s has been achieved experi-

mentally.

2. Experimental Setup

Figure 1 shows the experimental setup of the secure

optical communication system with chaos-masking. The

chaotic carrier is generated by optical feedback. The cir-

culator, optical coupler (OC), and the variable optical

attenuator (VOA) constitute the fiber-loop. The chaotic

carrier is then split into two paths by a 50:50 OC after

amplified by an Erbium-doped fiber amplifier (EDFA).

The upper path is used for encrypting the secure message

by CMS, and the lower path is transmitted as a secure

*This work is supported in part by the National Natural Science Foun-

dation of China (NSFC) under Grants 61071123, 61172059, and

6120122 4, the Funds for Ph. D. Studen t Academic New Investi gator of

Ministry of Education of China, and the Natural Science Foundation of

Changzhou City under CJ20 120015.

W. CHANG ET AL.

184

key. At the receiver, the two optical signals are detected

by two photodetectors (Discovery Semiconductor, DSC-

R401HG-39). Then, the message can be decrypted by

subtracting the secure key from the encrypted message.

The radio-frequency filter here is used to filter the extra

high-frequency noise. The digital storage oscilloscope

(Agilent DSO90404A) at the receiver-end is used for

real-time record of the synchronization between the two

chaotic signals and the decrypted message.

3. Chaotic Synchronization

The waveforms of the two chaotic signals without mes-

sage at the receiver are shown in Figure 2(a) and (b). It

can be seen that the synchronization of the system is well

achieved. The correlation coefficient of the two chaotic

signals is 0.9485, which provides a guarantee for the rea-

lization of the secure chaotic optical communication.

4. Effect of Wavelength Mismatch on the

Decrypti on Perf ormanc e

In the experiment of secure chaos-masking optical com-

munication, the continuous wave (CW) emitted by a

tunable laser (Thorlabs, TL1550-B) is modulated by a

Mach-Zehnder modulator (MZM). Then a 1.25-Gbits/s

optical message is ge nera ted. T he messa ge is hidde n into

a chaotic carrier by an OC, and launched into the fiber

for secure transmission. At the receiver, the message can

be decrypted by subtracting the secure key from the en-

crypted message. The wavelength of the message can be

changed by adjusting the wavelength of the tunable laser,

and ∆

is defined as the wavelength offset between the

wavelength of the message and that of the chaotic carrier

Figure 1. Experimental setup of the secure optical communication system with chaos-masking. DFB: distributed feedback

laser diode, OC: optical coupler, VOA: variable optical attenuator, EDFA: Erbium-doped fiber amplifier, PC: polarization

controller, MZM: Mac h-Zehnder modulator, PD: photodetecto r.

Figure 2 . Time domain wavefo rms of the t wo chaot ic signals w ithout message at t he receiver-end. (a) c haotic carrier w ithout

message, ( b) s ecure key.

W. CHANG ET AL.

185

Figure 3 . Recovered messag es wi th different ∆

. (a) - (e) are the o ptical spectr a of the encry pted messages, and the ∆

is set

to -0.15nm, -0.08nm, 0nm, 0.08nm, 0.15nm, respectively. (f) - (j) are the recovere d messages corres pond to different ∆

Figure 4. Experimental results of the secure chaotic optical communication with a 2.5-Gbits/s message when the ∆

is set to

0.12 nm. (a) chaotic carri er with a 2.5-Gbits/ s message, ( b) t he recovered messag e at t he receiver.

∆

m −

where

m and

c denote the wavelengths of the message

and that of the chaotic carrier, respectively. ∆

> 0

means the wavelength of the message is grater than that

of the chaotic carrier and vice versa. In the experiment,

the wa ve lengt h o f the messa g e is c ha n ge d t o ge t d i ffe rent

∆

, and then the decryption results are recorded

The experimental results are shown in Figure 3. It can

be seen that when ∆

= 0, which means the wavelength

of the message matches with that of the chaotic carrier,

the message recovered at the receiver is of bad quality.

When ∆

is less than zero, the quality of the recovered

message is improved. And a lager |∆

| means a better

result. W hen ∆

is greater than zero, the decryption per-

formance can also be improved. Comparing different

wavelength offset, it is found that the decryption perfor-

mance is better when ∆

is greater than zero.

5. High-speed Secure Chaotic Optical

Comm unication

In the secure chaos-masking optical communication sys-

tem, the larger the wavelength difference is, the better the

decryption performance is. However, a larger wavelength

difference will lead to less security of the message.

Therefore, it is necessary to consider both the security of

the message and the decryption performance of the re-

ceiver. A suitable wavelength offset will facilitate the

achievement of the high-speed secure communication.

When ∆

is set to 0.12 nm, the experimental results of

the secure chaotic optical communication with a 2.5-

Gbit s/s me ssa ge i s sho wn i n Figure 4. I t can be seen that

the message is safely hidden in the chaotic carrier and

well recovered at the receiver, which means the high-

speed secure communication is realized successfully.

W. CHANG ET AL.

186

6. Conclusions

In this paper, the mismatch of the wavelength between

the message and the chaotic carrier in the chaotic optical

communication with chaos-masking has been experi-

mentally investigated. The results show that the decryp-

tion performance of the receiver can be improved when

the wa velength of the message is greater than that of the

chaotic carrier. When the wavelength offset is set to 0.12

nm, high-speed secure communication with a message of

2.5 Gbits/s can be achieved. The results presented here

may provide some useful suggestions for the practical

applications of secure chaotic op tic a l c ommunications.

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