CN102025668B - High-speed method and device thereof for modulating multi-system light with minimum-frequency by shift keying - Google Patents

Abstract

The invention relates to a high-speed method and a device thereof for modulating multi-system light with minimum-frequency by shift keying. The method adopts the cascading mode of 2FSK (Frequency Shift Keying) and 2MSK (Minimum Shift Keying) to generate 4-system MSK signals, the first-stage modulation generates FSK signals the frequency difference of which is shown in the specification; the second-stage modulation splits the 2FSK signals to generate 4MSK signals with the frequency difference being 1/2TS and keep the continuous phase position. The method and the device realizing 4-system light MSK can generate 4-system light MSK signals with constant envelope, continuous phase position and strict orthogonality.

Description

High speed multi-system light Minimum Shift Keying Modulation method and device

Technical field

The present invention relates to a kind of high speed multi-system light Minimum Shift Keying Modulation method and device,, refer more particularly to a kind of high speed multi-system light Minimum Shift Keying Modulation method and device based on the cascade pattern.

Background technology

The research of format modulation signal is a large focus of current optical communication field, and new modulation format has caused people's concern to the improvement of transmission performance, especially at aspects such as suppressing nonlinear effect, raising dispersion tolerance and PMD tolerance limit, has obtained good effect.In optical fiber telecommunications system, the continuous light wave that light source sends or optical pulse train be carry information not, can only be as the carrier of information.Optical carrier is the signal relevant with polarization direction, signal amplitude, carrier frequency, carrier phase, if select in four amounts any one as the modulation parameter, just can form four kinds of modulation signals, respectively: Polarization Modulation (PolSK), amplitude modulation(PAM) (ASK), frequency modulation(FM) (FSK) and phase-modulation (PSK).

By signal loading, to light carrier, to form light signal, be exactly the major function of optical modulator.The mode that forms the optical frequency modulator is varied, but, with regard to the relation between modulator and light source, modulation technique can be divided into internal modulation technology and the large class of external modulation technology two.

The internal modulation technology is called again direct modulation technique, and the information that will transmit exactly changes current signal into sends into light source, obtains corresponding light signal output.Method commonly used is the bias current that changes laser, thereby obtains the amplitude modulation(PAM) of optical frequency.This modulation system is simple in structure, easily realizes, and be the common technology in the low speed optical fiber telecommunications system.But this internal modulation mode is difficult to realize High Speed Modulation, the one, due to the response speed restriction of semiconductor laser itself, the 2nd, this modulation system is accompanied with frequency chirp, makes the broadening of output signal spectrum, has limited the transmission capacity of system.

The external modulation technology refers to that light carrier is subject to the modulation of information signal in external modulator.Because being modulated at outside light source, this class realizes, therefore be called external modulation.Practical external modulator is based on the electrooptic modulator that the electro optic effect of crystal is made mostly.Can be divided into two classes: a class is based on the modulator of electric absorption effect, is called the EA modulator; Another kind of lithium niobate (the LiNbO that is based on ₃) performance of interferometric modulators, be called Mach-Zehnder (Mach-Zehnder) modulator.Wherein use the Mach-Zehnder modulator to realize the modulation of multiple digital form, such as the MSK modulation in the FSK modulation of the frequency shift keying (FSK) of differential phase keying (DPSK) (DPSK), difference four phase place phase shift keyings (DQPSK), noncontinuous phase and continuous phase.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind of modulator approach and device of realizing light 4MSK signal.

For solving the problems of the technologies described above, a kind of high speed multi-system light Minimum Shift Keying Modulation method, is characterized in that, described method adopts the cascade system of 2FSK and 2MSK to produce 4 system msk signals, and it is 1/T that first order modulation produces difference on the frequency _sfsk signal; The 2FSK signal is divided in second level modulation, and the generation difference on the frequency is 12T _sand can keep the continuous 4MSK signal of phase place.The modulated fsk signal obtained of the first order is

$E_{\mathrm{FSK}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)},$ The QMSK signal that the second level obtains is

$E_{\mathrm{QMSK}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)}\·\cos (\mathrm{\πRt}/2)e^{\mathrm{j\π}{q}_k(t-T_s)}\frac{E_{\mathrm{in}}}{4}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)}\·e^{-\mathrm{j\π}/2}\sin (\mathrm{\πRt}/2)e^{\mathrm{j\π}{p}_k(t-T_s)}$

Preferably, described 4MSK signal corresponding two paths of signals after interferometer subtracts each other, and then according to polarity, detects the true form that obtains upper and lower two-way.

A kind of multi-system of the high speed for said method light Minimum Shift Keying Modulation device, it is characterized in that, described device comprises serial-parallel converter, exclusive-OR operator, differential encoder, MZ modulator, delayer, phase shifter, and the upper and lower two-way of the first serial-parallel converter connects exclusive-OR operator, differential encoder, the second serial-parallel converter successively; Light carrier is divided into two-way after a MZ modulator, and a road is through the first delayer, and the Yu Shang mono-tunnel addition after the first phase shifter and MZ modulator of another road obtains the 2FSK signal, and wherein under the first serial-parallel converter, road is connected with MZ modulators modulate end; The 2FSK signal is divided into two-way after being input to the 3rd MZ modulator, one tunnel is through the second delayer and the 4th MZ modulator, another road is through the second phase shifter and MZ modulator, wherein the 4th MZ modulators modulate end is input as the second serial-parallel converter and sets out on a journey through the signal of the 3rd delayer, and MZ modulators modulate end is input as road signal under the second serial-parallel converter.

The invention has the beneficial effects as follows a kind of constant-envelope is provided, phase place continuously and the quaternary msk signal of strict orthogonal.

The accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments, technical scheme of the present invention is further described in detail.

Fig. 1 is light 4MSK modulation module structured flowchart;

The reception block diagram that Fig. 2 is light 4MSK signal.

Embodiment

As shown in Figure 1, it is divided into the two-stage modulation to light 4MSK modulation principle, and it is 1/T that first order modulation produces difference on the frequency _sfsk signal, it is 1/2T that second level modulation produces difference on the frequency _sthe QMSK signal.The modulated fsk signal obtained of the first order is

$E_{\mathrm{FSK}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)},$

The QMSK signal that the second level obtains is

$E_{\mathrm{QMSK}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)}\·\cos (\mathrm{\πRt}/2)e^{\mathrm{j\π}{q}_k(t-T_s)}\frac{E_{\mathrm{in}}}{4}{e}^{j(2\mathrm{\π}{f}_{0}t+c_k\left(t\right)\mathrm{\πt}/T_s)}\·e^{-\mathrm{j\π}/2}\sin (\mathrm{\πRt}/2)e^{\mathrm{j\π}{p}_k(t-T_s)}$ True form ak101 is divided into upper and lower two-way b through going here and there and changing _k102 and c _k103, b _k102 and c _k103 carry out obtaining d after XOR 104 _k105, obtaining e after differential coding _k107.CW110 is light carrier, and when light, after MZM1111, the light signal expression formula is:

$E_1\left(t\right)=-\frac{1}{2}{E}_{\mathrm{in}}\{{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\}=-E_{\mathrm{in}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\cos \left(\mathrm{\&pi;Rt}\right)---\left(1\right)$

R=1/T wherein _s, T _sfor element duration.The light signal of the upper arm of first order modulation is

$E_{\mathrm{lup}}\left(t\right)=-\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\&times;\cos [\mathrm{\&pi;R}(t-T_s/2)-\mathrm{\&pi;}/2]$

$=\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{e}^{e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="101217112223.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_0{T}_s/2}}\&times;\cos \left(\mathrm{\&pi;Rt}\right)---\left(2\right)$ The light signal of underarm is

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{1/\mathrm{low}}\left(t\right)=-\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{e}^{\mathrm{j\&phi;}}\&times;\sin \left(\mathrm{\&pi;Rt}\right)e^{j(\mathrm{\&pi;}/V_{\mathrm{\&pi;}}){\mathrm{Data}}_{\mathrm{ck}}\left(t\right)}$

$=-\frac{1}{\sqrt{2}}{E}_{\mathrm{in}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{e}^{\mathrm{j\&phi;}}\&times;\sin \left(\mathrm{\&pi;Rt}\right)e^{\mathrm{j\&pi;}{c}_k\left(t\right)}---\left(3\right)$

Need to introduce an additive phase φ 113 at underarm in formula (3), because 2 π f ₀t _s/ 2=2N π+δ, 0<δ<2 π, choose the value of suitable additive phase φ, makes δ-φ=pi/2, and the light signal of first order modulation output is like this

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{1\mathrm{out}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\cos \left(\mathrm{\&pi;Rt}\right)-\frac{E_{\mathrm{in}}}{2}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j{e}^{-\mathrm{j\&pi;}/2}\sin \left(\mathrm{\&pi;Rt}\right)e^{\mathrm{j\&pi;}{c}_k\left(t\right)}$

$=\frac{E_{\mathrm{in}}}{2}{e}^{j(2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)}=E_{\mathrm{FSK}}\left(t\right)---\left(4\right)$

The real part of formula (4) is

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{1\mathrm{out},\mathrm{real}}\left(t\right)=\frac{E_{\mathrm{in}}}{2}\cos \left(2{\mathrm{\&pi;f}}_{0}t\right)\cos \left(\mathrm{\&pi;Rt}\right)+\frac{E_{\mathrm{in}}}{2}\sin \left(2{\mathrm{\&pi;f}}_{0}t\right)\sin \left(\mathrm{\&pi;Rt}\right)\cos \left(\mathrm{\&pi;}{c}_k\left(t\right)\right)$

$=\frac{E_{\mathrm{in}}}{2}\cos (2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)---\left(5\right)$

In the modulated process of the second level of light signal, the expression formula of light signal after MZM4119 is:

$E_2\left(t\right)=-\frac{1}{2}{E}_{\mathrm{FSK}}\left(t\right)\{{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="101217112223.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="101217112223.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;Rt}/4}\}=-E_{\mathrm{FSK}}\left(t\right)\cos (\mathrm{\&pi;Rt}/2)---\left(6\right)$

The light signal of the upper arm of first order modulation is

${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{2\mathrm{up}}\left(t\right)=-\frac{1}{\sqrt{2}}{E}_{\mathrm{FSK}}\left(t\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="101217112223.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_0{T}_s-\mathrm{j\&pi;}/2}\&times;\cos [\mathrm{\&pi;R}(t-T_s)/2-\mathrm{\&pi;}/2]e^{j(\mathrm{\&pi;}/V_{\mathrm{\&pi;}}){\mathrm{Data}}_{\mathrm{qk}}(t-T_s)}$

$=\frac{1}{\sqrt{2}}{E}_{\mathrm{FSK}}\left(t\right)e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="101217112223.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;}{f}_0{T}_s-\mathrm{j\&pi;}/2}\&times;\cos (\mathrm{\&pi;Rt}/2)e^{j{\mathrm{\&pi;q}}_k(t-T_s)}---\left(7\right)$

The light signal of underarm is

${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{2\mathrm{low}}\left(t\right)=-\frac{1}{\sqrt{2}}{E}_{\mathrm{FSK}}\left(t\right)e^{-\mathrm{j\&pi;}/2}{e}^{j{\mathrm{\&phi;}}^{\&prime;}}\&times;\sin (\mathrm{\&pi;Rt}/2)e^{j(\mathrm{\&pi;}/V_{\mathrm{\&pi;}}){\mathrm{Data}}_{\mathrm{pk}}\left(t\right)}$

$=-\frac{1}{\sqrt{2}}{E}_{\mathrm{FSK}}\left(t\right)e^{-\mathrm{j\&pi;}/2}{e}^{j{\mathrm{\&phi;}}^{\&prime;}}\&times;\sin (\mathrm{\&pi;Rt}/2)e^{\mathrm{j\&pi;}{p}_k\left(t\right)}---\left(8\right)$

Need to introduce an additive phase φ ' 118 at underarm in formula (8), because 2 π f ₀t _s=2M π+δ ', 0<δ '<2 π, choose the value of suitable additive phase φ ', makes δ '-φ '=pi/2, like this light signal E of second level modulation output _4MSK(t) 123 are

$E_{4\mathrm{MSK}}\left(t\right)={\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{2\mathrm{out}}\left(t\right)=-\frac{1}{2}{E}_{\mathrm{FSK}}\left(t\right)\cos (\mathrm{\&pi;Rt}/2)e^{j{\mathrm{\&pi;q}}_k(t-T_s)}\frac{1}{2}{E}_{\mathrm{FSK}}\left(t\right)\sin (\mathrm{\&pi;Rt}/2)e^{j{\mathrm{\&pi;p}}_k\left(t\right)}$

$=\frac{E_{\mathrm{in}}}{4}{e}^{j(2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)}\&CenterDot;\cos (\mathrm{\&pi;Rt}/2)e^{\mathrm{j\&pi;}{q}_k(t-T_s)}\frac{E_{\mathrm{in}}}{4}{e}^{j(2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)}\&CenterDot;e^{\mathrm{j\&pi;}/2}\sin (\mathrm{\&pi;Rt}/2)e^{j{\mathrm{\&pi;p}}_k(t-T_s)}---\left(9\right)$

The real part of formula (9) is

${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="101217112223.png"\; state="\{\{state\}\}">E</figure-callout>}}_{2\mathrm{out},\mathrm{real}}\left(t\right)=\frac{E_{\mathrm{in}}}{4}\cos (2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)\&CenterDot;\cos (\mathrm{\&pi;Rt}/2)\cos \left({\mathrm{\&pi;q}}_k(t-T_s)\right)+$

$=\frac{E_{\mathrm{in}}}{4}\sin (2\mathrm{\&pi;}{f}_{0}t+c_k\left(t\right)\mathrm{\&pi;t}/T_s)\&CenterDot;\sin (\mathrm{\&pi;Rt}/2)\sin ({\mathrm{\&pi;q}}_k\left(t\right)-\mathrm{\&pi;}/2)---\left(10\right)$

Light 4MSK demodulation principle as shown in Figure 2

In figure

distribution of light intensity after interferometer is respectively

φ in formula (11) to (14) is the additive phase that each underarm is introduced, because 2 π f ₀t _s/ 2=2N π+δ, 0<δ<2 π, choose the value of suitable additive phase φ, makes φ+δ=0, like this u _kand v _kvalue as follows

Wherein

u _kbe used for detecting true form c _k, v _kbe used for detecting true form b _k.Because in the 4MSK modulation, process T when true form is 00,01,11 and 10 _sadditive phase be respectively-3 π ,-π, π and 3 π, pass through T _s/ 2 additive phase be respectively-3 pi/2s ,-pi/2, pi/2 and 3 pi/2s, again due to sin (pi/2)=sin (3 pi/2)=1, sin (pi/2)=sin (3 pi/2)=-1, cos (pi/2)=cos (pi/2)=1 and cos (3 pi/2)=cos (3 pi/2)=-1, so according to u _kand v _kpolarity just can detect true form c _kand b _kvalue, anodal corresponding true form is 1, the corresponding true form of negative pole is 0.

Also comprise in accompanying drawing 1 that 106 for the differential coding module, 108 is string modular converter, and 109,112 and 117 is Postponement module, and 114,116,120 and 121 is the Mach-Zehnder interferometer module, and 115 is first order FSK output, and 122 is second level 4MSK output.Also comprise in accompanying drawing 2 that 201 for the 4MSK input signal, 202,203 and 204 is Postponement module, and 205 is the photodetector module, and 206,207 is the plus and minus calculation module.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although with reference to preferred embodiment, the present invention is had been described in detail, those of ordinary skill in the art is to be understood that, can modify or be equal to replacement technical scheme of the present invention, and not breaking away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.

Claims (2)

1. a high speed multi-system light Minimum Shift Keying Modulation method, is characterized in that, described method adopts the cascade system of 2FSK and 2MSK to produce 4 system msk signals, and it is 1/T that first order modulation produces difference on the frequency _sfsk signal; The 2FSK signal is divided in second level modulation, and the generation difference on the frequency is 1/2T _sand can keep the continuous 4MSK signal of phase place; Described 4MSK signal corresponding two paths of signals after interferometer subtracts each other, and then according to polarity, detects the true form that obtains upper and lower two-way, i.e. process T when true form is 00,01,11 and 10 _sadditive phase be respectively-3 π ,-π, π and 3 π, pass through T _s/ 2 additive phase be respectively-3 pi/2s ,-pi/2, pi/2 and 3 pi/2s, so according to u _kand v _kpolarity just can detect true form c _kand b _kvalue, anodal corresponding true form is 1, the corresponding true form of negative pole is 0; Wherein, u _kfor comprising c _kand b _k4 system msk signals corresponding two paths of signals after interferometer subtract each other the polarity obtained at upper branch road, v _kfor comprising c _kand b _k4 system msk signals corresponding two paths of signals after interferometer subtract each other the polarity obtained at lower branch road.

2. the multi-system of the high speed for the described method of claim 1 a light Minimum Shift Keying Modulation device, it is characterized in that, described device comprises serial-parallel converter, exclusive-OR operator, differential encoder, MZ modulator, delayer, phase shifter, and the upper and lower two-way of the first serial-parallel converter connects exclusive-OR operator, differential encoder, the second serial-parallel converter successively; Light carrier is divided into two-way after a MZ modulator, one tunnel is through the first delayer, the Yu Shang mono-tunnel addition after the first phase shifter and the 2nd MZ modulator of another road obtains the 2FSK signal, and wherein under the first serial-parallel converter, road is connected with the 2nd MZ modulators modulate end; The 2FSK signal is divided into two-way after being input to the 3rd MZ modulator, one tunnel is through the second delayer and the 4th MZ modulator, another road is through the second phase shifter and the 5th MZ modulator, wherein the 4th MZ modulators modulate end is input as the second serial-parallel converter and sets out on a journey through the signal of the 3rd delayer, and the 5th MZ modulators modulate end is input as road signal under the second serial-parallel converter.

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