CN103188070A - Optical chaotic sequence generator - Google Patents

Abstract

The invention discloses an optical chaotic sequence generator, wherein chaotic sequence is already used in a wireless CDMA (code division multiple access) system due to the advantages of good security, relevance and high quantity, and lots of theories and experiment research reports are provided; and how to generate and apply chaotic sequence in an optical code division multiple access (OCDMA) system arouses the interests and attentions of people. The invention discloses a method for generating a simulated bipolar chaos sequence in an optical domain, wherein the amplitude and phase of the electric field vector of an input light can be modulated via a Mach-Zehnder interferometer; the electric field vector of an output light can be equal to the product of the electric field vector of the input light and a cosine item by controlling the phase shift caused by the two arms of the interferometer; and a plurality of the interferometers can be combined with an optical fibre delay line and a phase shifter to generate a bipolar chaotic sequence according to logistic mapping, and form the chaotic sequence generator. The chaotic sequence generator can be used in an OCDMA system, so as to increase the capacity and improve the security of the system.

Description

A kind of optical chaos sequencer

Technical field

The invention belongs to the communications field, relate in particular to a kind of full optical device that can produce chaos sequence.

Background technology

Chaos is deterministic in the non linear system, similar phenomenon at random, and it is very responsive to the variation of initial value.Chaotic signal has good correlation and confidentiality, and have wide power spectrum, like noise, characteristics such as renewable, the chaos sequence that utilizes chaos system to produce is suitable as the frequency expansion sequence in the cdma system very much.In the radio CDMA field, how existing a large amount of theories and experimental study report utilize chaos system to produce the chaos sequence with good correlation, become a brand-new and significant research direction and inquire into generation and the application of chaos sequence in the OCDMA system.

There is document to propose a kind of method that produces the unipolarity sequence of light intensity chaos change, and applies it in the OCDMA system, to improve the fail safe of communication.But the correlation of this unipolarity sequence is relatively poor, and multiple access disturbs big, and the number of users of connecting system is very limited simultaneously.Mach-increase amplitude and phase place that the Dare interferometer can be modulated input optical electric field vector, we have designed the full optical device that produces simulated dual polarity chaos sequence to utilize this principle.

Summary of the invention

The objective of the invention is a kind of generator that can produce simulated dual polarity chaos sequence in the light territory.

Mach-increase the Dare interferometer can modulate amplitude and the phase place of importing the optical electric field vector, by controlling the phase shift that interferometer two arms cause, can make the electric field intensity of exporting light equal to import the product of optical electric field vector and cosine term, a plurality of interferometers can produce ambipolar chaos sequence by the logistic mapping in conjunction with fibre delay line and phase-shifter, form chaos sequence generator.This chaos sequence generator can be used for the OCDMA system, to improve capacity and the confidentiality of system.

Description of drawings

Fig. 1 increases Dare interferometer schematic diagram for Mach;

Fig. 2 Mach of serving as reasons increases the optical chaos sequencer that Dare interferometer and fibre delay line and phase-shifter constitute.

Embodiment

The present invention is a kind of full optical device that can produce simulated dual polarity chaos sequence, and its operation principle is as described below:

1.Logistic mapping and character thereof

The Chebeshev multinomial is T _m(x), m 〉=2, wherein, T ₂(x)=2x ²-1, T ₃(x)=4x ³-3x, The Chebeshev multinomial has character: T _m[cos (θ)]=cos (m θ) ^[2]Be mapped as x by its Logistic that constitutes _N+1=T _m(x _n), x _n∈ [1,1].Work as x _nDuring=cos (θ), x _N+1=cos (m θ).

2. with Mach-the increase bipolarity chaos sequence that the Dare interferometer produces simulation

Mach-increase the electric field that the Dare interferometer can be modulated input light, its structure as shown in Figure 1.If the electric field strength of input light is:

E _i＝Ae ^iωti _l (1)

A is the amplitude of electric field, and ω is the angular frequency of light, i _lUnit vector on the expression polarization direction, luminous power is:

$E_i\·E_i^{*}=A^2---\left(2\right)$

Through after first three-dB coupler, input light is divided into two bundles, and every optical power beam is:

P _i1＝P _i2＝A ²/2 (3)

If after two arms transmitted up and down, the polarization direction of two-beam remained unchanged, then electric field strength can be expressed as respectively:

$E_1=\frac{A}{\sqrt{2}}{e}^{i(\mathrm{\ωt}-{\mathrm{\φ}}_1)}{i}_l---\left(4\right)$

$E_2=\frac{A}{\sqrt{2}}{e}^{i(\mathrm{\ωt}-{\mathrm{\φ}}_2)}{i}_l---\left(5\right)$

φ ₁And φ ₂It is respectively the phase shift that interferometer two arms cause.Behind second coupler, total electric field intensity is:

$E=E_1+E_2$

$=\frac{A}{\sqrt{2}}[e^{i(\mathrm{\ωt}-{\mathrm{\φ}}_1)}{i}_l+e^{i(\mathrm{\ωt}-{\mathrm{\φ}}_2)}{i}_l]$

$=\frac{A}{\sqrt{2}}{e}^{\mathrm{i\ωt}}[\cos {\mathrm{\φ}}_1+\cos {\mathrm{\φ}}_2+i(\sin {\mathrm{\φ}}_1+\sin {\mathrm{\φ}}_2)]i_l---\left(6\right)$

Make sin φ ₁+ sin φ ₂=0, then the phase place that causes respectively of two arms changes φ ₁And φ ₂Should satisfy:

φ ₁+φ ₂＝2kπ (7)

Perhaps φ ₁-φ ₂=2k π+π (k=1,2,3...) (8)

Cos φ when (8) formula is set up ₁+ cos φ ₂=0, so do not consider this situation.When (7) formula was set up, output optical electric field intensity was:

$E=\sqrt{2}\left[\cos {\mathrm{\φ}}_1\right]A{e}^{\mathrm{i\ωt}}{i}_l---\left(9\right)$

Fig. 2 is N Mach-the increase chaos sequence generator schematic diagram that the Dare interferometer constitutes, and behind each Mach-increase the Dare interferometer fibre delay line and phase-shifter is arranged.Behind the coupler of incident light through a 1 * N, each branch road obtains same power, and the phase shift that two arms of Mach-increase Dare interferometer cause satisfies condition:

φ _(i+l)1＝mφ _i1 (10)

And the phase shift that two arms of each interferometer cause is respectively satisfied:

φ _i1+φ _i2＝2kπ (11)

Fibre delay line is sent to corresponding position with light pulse, and phase-shifter is used for offsetting the phase shift that fibre delay line causes.At this moment, Mach-the increase electric field strength E of Dare interferometer output ₁, E ₂..., E _NIt is the bipolarity chaos sequence that produces according to the logistic mapping.

Claims (4)

1. an optical chaos sequencer is characterized in that it comprises the steps:

Step 1 is shone upon by Chebeshev polynomial construction Logistic;

Step 2, control Mach-increase the phase shift that Dare interferometer two arms cause makes the electric field intensity of exporting light equal to import the product of optical electric field vector and cosine term;

Step 3, a plurality of Mach-increase the Dare interferometer to produce ambipolar chaos sequence in conjunction with fibre delay line and phase-shifter by the logistic mapping form chaos sequence generator.

2. a kind of optical chaos sequencer according to claim 1 is characterized in that: in step 1, by the Logistic mapping of Chebeshev polynomial construction, satisfy character: work as x _nDuring=cos (θ), x _N+1=cos (m θ).

3. a kind of optical chaos sequencer according to claim 1, it is characterized in that: in step 2, Mach-the increase phase shift that Dare interferometer two arms cause and be the integral multiple of 2 π, the electric field intensity that can export light through derivation equals to import the product of optical electric field vector and cosine term like this.

4. a kind of optical chaos sequencer according to claim 1, it is characterized in that: in step 3, Mach-increase the phase shift that Dare interferometer two arms cause is some particular values, fibre delay line is sent to corresponding position with light pulse, phase-shifter is used for offsetting the phase shift that fibre delay line causes, Gou Zao optical chaos sequencer can produce ambipolar chaos sequence by the logistic mapping thus.

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