CN102624460A - Modulator for optical fibre linear transmission and third-order intermodulation suppression method for modulator - Google Patents

Abstract

The invention discloses a modulator for optical fibre linear transmission and a third-order intermodulation suppression method for the modulator, belonging to the field of optical communication. The method comprises the following steps of: (1) inputting carrier signals in an MZM1 (Mach-Zehnder modulator 1) and an MZM2 respectively according to a ratio of n3: 1; (2) inputting radio-frequency signals in the two MZMs according to an amplitude ratio of 1: n; and (3) adjusting the two MZMs to cause optical signals to be orthogonal signals mutually, and then combining and outputting; wherein the phases of the radio-frequency signals RF input in the two MZMs are opposite, or the working orthogonal offset points are different, or the output signals are combined and output by using a differential detector; if the combining ratio of the MZM1 and the MZM2 is n3: 1, then n ranges from 1.8 to 3.7; if the combining ratio of the MZM1 and the MZM2 is 1: 1, then n is 2. The structure optionally comprises a laser, a coupler with a ratio of n3: 1, two linear modulators, a coupler 2, a phase shifter and a photoelectric detector. The modulator for optical fibre linear transmission and the third-order intermodulation suppression method for the modulator disclosed by the invention greatly improve the third-order intermodulation suppression effect for optical fibre linear transmission.

Description

A kind of linear transmission modulator and third order intermodulation inhibition method thereof

Technical field

The present invention relates to a kind of linear transmission modulator and third order intermodulation inhibition method thereof, belong to optical communication field.

Background technology

Radiofrequency signal optical fiber transmission technique (Radio-over-Fiber is called for short RoF) is a key technology in the modern optical communication technology, in the communications field number of applications is arranged.Need radiofrequency signal (Radio Frequency is called for short the RF signal) be transferred to the destination as far as possible undistortedly in this transmission course, the committed step that wherein relates to is exactly the linear modulation and the linear demodulation of RF signal.The main linear modulator that adopts at present increases Dare modulator (Mach-Zehnder Modulator for Mach; Be called for short MZM); The main feature of this modulator is the ideal sinusoidal curve for its adjustment curve, selects suitable operating bias point can realize the inhibition fully of the even order distortion of input rf signal as external modulator.For the odd-order signal; The single order signal is effective RF signal; Required power is big as far as possible; Three rank signals comprise third order intermodulation signal and the harmonic signal that the RF signal produces, third order intermodulation signal wherein since can drop on RF signal identical frequency band in can produce the linear distortion influence to the RF signal that receives, therefore need suppress it.

The present invention is the basis with multiple present existing linear transfer technology, and the nonlinear distortion that proposes multiple new-type practicability suppresses technical scheme, and the concrete parameter in the system work process has been carried out the more accurate demonstration of calculating.

As shown in Figure 1; Modulator utilizes two light sources to inject among the patent application US5031235A; Realize the inhibition of even order distorted signal through selecting suitable bias point; Through two light source output power ratios of adjustment, make the opposite third order intermodulation signal of two-way generation amplitude same phase up and down again, suppress so that carry out third order intermodulation at receiving terminal.

As shown in Figure 2, patent application EP1056228A2, nonlinear distortion suppresses technological system, carries out the nonlinear distortion inhibition with two light sources with different output wavelengths through wavelength division multiplexing/wavelength-division demultiplexing mode.Through selecting the suitable bias point of MZM to suppress the even order distortion that input rf signal produces, carry out the identical third order intermodulation signal of RF signal modulation generation amplitude through two wavelength, adopt the Differential Detection mode to suppress third order intermodulation at receiving terminal.

As shown in Figure 3; UCLA linear transfer scheme is offset to minimum bias point with modulator; To obtain best useful signal utilance, the amplitude that gets into the two paths of signals of modulator through adjustment realizes that the third order intermodulation amplitude same phase of two paths of signals is opposite, carries out coherent reception at receiving terminal; Obtain through the signal transmission RF signal after the third order intermodulation inhibition, employed modulator cut-away view is as shown in Figure 4 among the linear transfer figure.

Only carry out the modulation of RF signal in Tsing-Hua University's linear transfer scheme to one among two MZM up and down; Through adjusting the linear transfer of the relation realization RF signal between three operating bias points among two parallel MZM (DPMZM), its linear transfer system principle sketch map is as shown in Figure 5.

Summary of the invention

To the technical problem that exists in the prior art, the object of the present invention is to provide a kind of linear transmission third order intermodulation inhibition method.The linear transmission method that proposes among the present invention is exactly to the MZM applicable cases, the technology that third order intermodulation is suppressed.Through selecting suitable MZM operating bias point to suppress the even order distortion; Suppress technology through third order intermodulation again and suppress third order distortion; This linear transfer system will be limited by five rank linear distortions only thus, and system can realize the high linearity modulation this moment, thereby realize high linear RF signal transmission.

Through to neutral line transmission system of the present invention analyze can know detect the single order signal strength signal intensity:

${\tilde{I}}_{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">S</figure-callout>}1}=[\frac{1}{2}{E}_I^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}(m_1-\frac{3}{8}{\mathrm{<figure-callout\; id="1"\; label="m"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">m</figure-callout>}}_1^3){\sin \mathrm{\&phi;}}_1\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="r\; d"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">r</figure-callout>}}_d+\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="E\; I"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">E</figure-callout>}}_I^{}{\sin }^2\mathrm{\&alpha;}{\sin }^2\mathrm{\&beta;}(m_2-\frac{3}{8}{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">m</figure-callout>}}_2^3){\sin \mathrm{\&phi;}}_2\&CenterDot;r_{d2}]({\cos \mathrm{\&omega;}}_{1}t+{\cos \mathrm{\&omega;}}_{2}t)$

Three rank signal strength signal intensities:

${\tilde{I}}_{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">S</figure-callout>}3}=[-\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="E\; I"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">E</figure-callout>}}_I^{}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}\left(\frac{{\mathrm{<figure-callout\; id="1"\; label="m"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">m</figure-callout>}}_1^3}{8}\right){\sin \mathrm{\&phi;}}_1\&CenterDot;r_{d1}-\frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="E\; I"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">E</figure-callout>}}_I^{}{\sin }^2\mathrm{\&alpha;}{\sin }^2\mathrm{\&beta;}\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">m</figure-callout>}}_2^3}{8}\right){\sin \mathrm{\&phi;}}_2\&CenterDot;r_{d2}][\cos (2{\mathrm{\&omega;}}_1-{\mathrm{\&omega;}}_2)t+\cos ({2\mathrm{\&omega;}}_t-{\mathrm{\&omega;}}_1)t]$

Cross term:

$I_X=-{2E}_I^2\sin \left(\frac{{\mathrm{\&phi;}}_{\mathrm{RF}1}\left(t\right)+{\mathrm{\&phi;}}_1}{2}\right)\sin \left(\frac{{\mathrm{\&phi;}}_{\mathrm{RF}2}\left(t\right)+{\mathrm{\&phi;}}_2}{2}\right)\cos \mathrm{\&alpha;}\cos \mathrm{\&beta;}\sin \mathrm{\&alpha;}\sin \mathrm{\&beta;}\&CenterDot;r_d\&CenterDot;{\cos \mathrm{\&phi;}}_3\&CenterDot;{\cos \mathrm{\&delta;}}_{\mathrm{polar}}$

Therefore the third order intermodulation rejection condition is:

${\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="m"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">m</figure-callout>}}_1^3{\sin \mathrm{\&phi;}}_1\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="r\; d"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">r</figure-callout>}}_d+{\sin }^2\mathrm{\&alpha;}{\sin }^2\mathrm{\&beta;}\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">m</figure-callout>}}_2^3{\sin \mathrm{\&phi;}}_2\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="r\; d"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">r</figure-callout>}}_d=0$

Should guarantee that the single order signal amplitude is big as far as possible this moment.Wherein, M1 and m2 are the RF signal modulation degree of two modulators; Rd1 and rd2 are the responsiveness (rd1=rd2 when using same photoelectric detector of the photoelectric detector that injects at receiving terminal of two ways of optical signals up and down; Rd1=-rd2 when adopting difference detector), α and β are respectively and adopt the equivalent and next coupler splitting of trigonometric function than parameter, and be as shown in Figure 6.

Above-mentioned cross term does not have benefit to effective RF signal transmission, need suppress.Two-way up and down, i.e. MZM1,2 two-way, light signal is adjusted to the inhibition that orthogonal signalling can realize cross term, and the concrete approach that suppresses can adopt three kinds:

(1) regulates two ways of optical signals phase difference 3=π n/2 (n=± 1, ± 3, ± 5 up and down ...).

(2) regulate two ways of optical signals polarization angle difference δ up and down _PloarAfter this=pi/2 proposes for taking the lead in to the palarization multiplexing scheme in the present invention.

(3) use independent light electro-detection path, avoid up and down the two ways of optical signals generation cross term that influences each other.

Make the input radio frequency signal amplitude that following relation is arranged:

V _RF2=γ ^-1V _RF1Be m ₂=γ ^-1m ₁(0＜| γ |＜1)

Can get by the third order intermodulation rejection condition:

$\mathrm{\&gamma;}={\left(\frac{{\sin }^2\mathrm{\&alpha;}{\sin }^2\mathrm{\&beta;}}{{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}}\right)}^{1/3}{(-\frac{{\sin \mathrm{\&phi;}}_1\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="r\; d"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">r</figure-callout>}}_d}{{\sin \mathrm{\&phi;}}_2\&CenterDot;r_{d2}})}^{1/3}$

The sign factor of determination of definition γ is:

$\mathrm{sign}\&equiv;{(-\frac{{\sin \mathrm{\&phi;}}_1\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="r\; d"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">r</figure-callout>}}_d}{{\sin \mathrm{\&phi;}}_2\&CenterDot;r_{d2}})}^{1/3}$

Then:

$\mathrm{\&gamma;}={\left(\frac{{\sin }^2\mathrm{\&alpha;}{\sin }^2\mathrm{\&beta;}}{{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&beta;}}\right)}^{1/3}\&CenterDot;\mathrm{sign}$

For second order signal (second order intermodulation, second-order distortion) is suppressed fully, so that carry out broadband application, therefore two modulators all need be operated in the quadrature bias point.

Can get by the sign parameter-definition; The sign value is by the connected mode decision of bias point φ 1 and φ 2 and photoelectric detector; Because bias point is the quadrature bias point; Therefore sin φ 1 can value be+1 or-1 all with sin φ 2, rd1/rd2=1 when using same photoelectric detector, rd1/rd2=-1 when adopting difference detector.When sign=1, γ＞0, this moment m1 and m2 jack per line, i.e. the RF signal phase unanimity of two modulators input; When sign=-1, γ＜0, this moment m1 and m2 opposite sign, promptly the RF signal phase imported of two modulators is opposite.Therefore, realize that third order intermodulation suppresses to have three kinds of approach:

The RF signal phase of (1) two modulator input is opposite.

The work quadrature bias point of (2) two modulators is different.

(3) adopt Differential Detection.

More than three kinds of approach have only one satisfy or condition that three are satisfied simultaneously under, can realize that third order intermodulation suppresses.

Because the sign values of parameters does not have the essence influence to " the best effort scope " described in the present invention, in following explanation, all getting sign=1 is condition of work.

Condition of work one

Get β=α (light ratio of closing of two-way luminous power equals splitting ratio up and down), get

Get A=sin ²α

Because (0＜γ＜1) is so (0＜A＜1/2)

This moment, the single order signal amplitude was:

$\left|{\tilde{P}}_{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">S</figure-callout>}1}\right|=\frac{1}{2}{E}_I^2[-A^2+{(1-A)}^{\frac{4}{3}}\&CenterDot;A^{\frac{2}{3}}]m_2$ $F\left(A\right)={-A}^2+{(1-A)}^{\frac{4}{3}}\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA0000146631760000022.png,HDA0000146631760000023.png"\; state="\{\{state\}\}">A</figure-callout>}}^{\frac{2}{3}}$

Relation between optical coupler splitting ratio and the amplitude output signal is shown in figure 10.

Can get single order signal amplitude maximum when A=0.199～0.209 thus

This moment sin ²α → 0.2 cos ²α → 0.8 γ ^-1=2.4286～2.5304

(reach the γ of the following stated here ^-1Be follow-up described ratio n among the present invention)

Can get simultaneously, single order signal amplitude deterioration is in the 0.5dB scope when A=0.123～0.292

This moment, two-way RF signal amplitude was γ than desirable wider range up and down ^-1=1.8048～3.7045

Searched out the best effort scope (scope of two-way input rf signal amplitude ratio γ and corresponding with it splitting ratio scope up and down) during the parallelly connected MZM modulator structure of this kind linear transfer is used thus

Condition of work two

Get (two paths of signals closes the road according to 1: 1 equal proportion up and down), get

Get A=sin ²α

Because (0＜γ＜1) is so (0＜A＜1/2)

This moment, the single order signal amplitude was:

$\left|{\tilde{P}}_{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">S</figure-callout>}1}\right|=\frac{1}{4}{E}_I^2[-A+{(1-A)}^{\frac{2}{3}}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">A</figure-callout>}}^{\frac{1}{3}}]$ $F\left(A\right)=-A+{(1-A)}^{\frac{2}{3}}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="A"\; filenames="HDA0000146631760000023.png,HDA0000146631760000031.png"\; state="\{\{state\}\}">A</figure-callout>}}^{\frac{1}{3}}$ Differentiate gets $A=\frac{1}{9}$ The time get maximum; Relation between optical coupler splitting ratio and the amplitude output signal is shown in figure 11.

Can get single order signal amplitude maximum

when A=0.11 thus

This moment sin ²α → 0.11 cos ²α → 0.89 γ ^-1=2

Can get simultaneously, single order signal amplitude deterioration is in the 0.5dB scope when A=0.045～0.207

This moment, two-way RF signal amplitude was γ than desirable wider range up and down ^-1=1.5647～2.7686

Searched out the optimum Working point during the parallelly connected MZM modulator structure of this kind linear transfer is used thus, promptly the two paths of signals splitting ratio is that two-way RF signal input range ratio is 1: 2 about 8: 1 whiles up and down.In addition, condition of work two is compared with condition of work one, and maximum single order signal amplitude is lower slightly under the third order intermodulation rejection condition, but because to close light ratio be 1: 1, thus system realize easier.

The present invention is with the maximum difference of related patent U.S. Patent No. technology in the past: the present invention clearly adopts the best effort range of condition to carry out non-linear inhibition, proposes the mutual distracter of two ways of optical signals is eliminated in influence from novel back to the polarized orthogonal multiplexing scheme simultaneously.Idiographic flow is: the optical carrier of laser output carries out beam split through the coupler of special ratios, in two-way light path up and down, obtains the optical carrier of certain power ratio; Simultaneously, the RF signal with special ratios is input to respectively among two MZM in the two-way up and down, to obtain the opposite third order intermodulation signal of specific amplitude ratio and phase place; The two-way light path is closed the road through the optical coupler of special ratios up and down, and to obtain the third order intermodulation signal that amplitude is identical and phase place is opposite, the third order intermodulation signal is cancelled out each other owing to the amplitude same phase on the contrary behind the ECDC road, thereby obtains the signal that three rank suppress.Final purpose in this flow process is that when suppressing three rank signals, keeping the single order signal to greatest extent is effective reception end RF restituted signal.The special ratios of the special ratios of the coupler in this flow process and RF signal is one to one; It has best working range, promptly can under the complete rejection condition of third order intermodulation, make the single order signal amplitude remain on the scope of the coupler ratio/RF signal proportion in the deterioration 0.5dB scope.This best operating condition scope was not carried out quantitative Analysis and application in the prior art.

Compared with prior art, good effect of the present invention

The advantage that linear transfer scheme described in the present invention is total:

third order distortion suppresses amplitude, and when two-way input rf signal ratio is insensitive to the beam split in this linear transfer system, can reduce the device making technics requirement.Difference input range ratio 1 in two MZM: the RF signal of n, the luminous power ratio that gets into MZM adopts n ³: 1; Among the present invention condition of work once the n span can be in 1.8048～3.7045 scopes value guarantee suppressing under the third order intermodulation situation output single order Signal Degrade in the 0.5dB scope (two times n spans of condition of work can be in 1.5647～2.7686 scopes value guarantee suppressing under the third order intermodulation situation output single order Signal Degrade in the 0.5dB scope), this n span is this type of linear transfer scheme best effort scope.

realizes that through three kinds of modes the useless cross term of two-way suppresses up and down: light phase difference regulative mode, back are to polarized orthogonal multiplex mode, independent light electro-detection path mode.Wherein the back proposes for taking the lead in to the polarized orthogonal multiplex mode, does not still have same scheme both at home and abroad.

The four kinds of linear transfer schemes of the following stated and the common difference characteristics of prior art are: the core work condition of these four kinds of inhibition third order intermodulations that scheme adopted is the linear transfer scheme best effort scope described in the present invention, i.e. the special ratios scope of coupler and the special ratios scope of RF signal one to one with it.Below four kinds of linear transfer schemes expanded application of best effort scope for this reason; As the light source special ratios beam split described in will inventing replaces with two light sources (scheme four), the light territory signal stack in will inventing replaces with electric territory stack (scheme three, four), and its basic thought does not have essential distinction.

Linear transfer scheme (one) advantage:

realizes that the linear transfer system configuration is simple; The number of devices that is adopted is few; Be convenient to integrated application; Cost is low, and processing technology can satisfy at present.

Linear transfer scheme (two) advantage:

adopts the back to the polarized orthogonal multiplexing scheme; Use polarization rotator spare to realize two paths of signals quadrature up and down, eliminate useless cross term signal and disturb.Polarization rotator spare is relatively stable, and light sources with different wavelengths all is suitable for, and need not to control.

The advantage of linear transfer scheme (three):

adopts electric territory Differential Detection mode to carry out the third order distortion inhibition; Need not two paths of signals is up and down carried out accurate phase difference control or polarization rotation, require lower transmission system.

The advantage of linear transfer scheme (four):

adopts electric territory Differential Detection mode to carry out the third order distortion inhibition; Need not two paths of signals is up and down carried out accurate phase difference control, require lower transmission system.

uses two lasers as light source; Realize the accurate control of luminous power ratio; Coupler splitting than manufacture craft no requirement (NR), need not customized specific splitting ratio coupler.

Description of drawings

Fig. 1 line type light modulator;

Fig. 2 nonlinear distortion suppresses technology;

Fig. 3 linear transfer block diagram;

Employed modulator cut-away view among Fig. 4 linear transfer figure;

Fig. 5 linear transfer system principle sketch map;

Fig. 6 superlinearity transmission plan one block diagram;

Fig. 7 superlinearity transmission plan two block diagrams;

Fig. 8 superlinearity transmission plan three block diagrams;

Fig. 9 superlinearity transmission plan four block diagrams;

Relation between Figure 10 condition of work optical coupler splitting ratio in a period of time and the amplitude output signal;

Relation between two time of Figure 11 condition of work coupler splitting ratio and the amplitude output signal.

Embodiment

Below in conjunction with accompanying drawing particular content of the present invention is explained in further detail:

Scheme one basic functional principle

As shown in Figure 6, concrete annexation is: the optical carrier of laser output is injected into the input of the coupler with specific beam split ratio; Among the MZM about optical carrier after the beam split of process special ratios is injected into respectively after the output of coupler output the two-way; The RF signal of while two-way specific amplitude ratio is input to the RF input of corresponding MZM and modulates, and two MZM connect the operating bias point of bias point controller (V1/V2) with control MZM respectively; Light signal after modulate through the RF signal on following road carries out phase adjusted through phase shifter, to make it and to set out on a journey through the quadrature in phase of the light signal after the modulation of RF signal; Two paths of signals after regulating through phase difference is input in the coupler of specific beam split ratio and closes the road; The light signal that closes behind the road is injected in the photoelectric detector, and the RF that can obtain suppressing through three rank receives signal.

The scheme agent structure adopts parallelly connected MZM mode, and (two-way ratio 1 up and down: n) in two MZM, to import the RF signal of different amplitudes respectively.Carrier signal was carried out beam splitting before getting into MZM, power beam splitting ratio adopts two-way n up and down ³: 1 mode (is n ³: the more powerful signal of 1 coupler output road output is connected with the MZM1 input; The MZM1 branch road is called sets out on a journey; Compensation road output of another output smaller power is connected with the input of MZM2, and the MZM2 branch road is called down road, makes carrier power among MZM1 and the MZM2 than being n ³: 1), in the RF signal that injects different amplitudes, can produce three onesize rank effects like this.Phase shifter Φ 3 roles are that differing of two paths of signals become 90 °, and two paths of signals is mutually orthogonal about can making like this, does not produce useless cross term.Two-way is because the amplitude of the RF signal of input is different up and down, and the RF signal can't be cancelled out each other fully, thereby realizes high SFDR performance index.Two-way is based on γ and sign relation are provided with condition of work as previously mentioned up and down.

Scheme two basic functional principle

As shown in Figure 7, use the back to the polarized orthogonal multiplexing scheme, concrete annexation is: the optical carrier of laser output is injected into the input of the coupler with specific beam split ratio; Among the MZM about optical carrier after the beam split of process special ratios is injected into respectively after the output of coupler output the two-way; The RF signal of while two-way specific amplitude ratio is input to the RF input of corresponding MZM and modulates, and two MZM connect the operating bias point of bias point controller (V1/V2) with control MZM respectively; Light signal after modulate through the RF signal on following road carries out polarization state through polarization rotator spare to be regulated, to make it and to set out on a journey through the polarization state quadrature of the light signal after the modulation of RF signal; Two paths of signals after the process polarization is regulated is input to and closes the road in the polarization beam combiner; The light signal that closes behind the road is injected in the photoelectric detector, and the RF that can obtain suppressing through three rank receives signal.

The scheme agent structure adopts parallelly connected MZM mode, and (two-way ratio 1 up and down: n), carrier signal was carried out beam splitting before getting into MZM, and power beam splitting ratio adopts n in two MZM, to import the RF signal of different amplitudes respectively ³: 1 mode (is n ³: the more powerful signal of 1 coupler output road output is connected with the MZM1 input; The MZM1 branch road is called sets out on a journey; Compensation road output of another output smaller power is connected with the input of MZM2, and the MZM2 branch road is called down road, makes carrier power among MZM1 and the MZM2 than being n ³: 1), in the RF signal that injects different amplitudes, can produce three onesize rank effects like this.Following road signal is through the polarization rotator spare signal state of polarization quadrature that polarization state rotated to be and set out on a journey, and passes through polarization mixer (PBC) coupling again and is injected in the photoelectric detector and detects, and can making up and down like this, two paths of signals does not produce useless cross term.Two-way is because the amplitude of the RF signal of input is different up and down, and the RF signal can't be cancelled out each other fully, thereby realizes high SFDR performance index.Two-way is provided with condition of work according to γ and sign relation as previously mentioned up and down.

Scheme three basic functional principle

As shown in Figure 8, concrete annexation is: the optical carrier of laser output is injected into the input of the coupler with specific beam split ratio; Among the MZM about optical carrier after the beam split of process special ratios is injected into respectively after the output of coupler output the two-way; The RF signal of while two-way specific amplitude ratio is input to the RF input of corresponding MZM and modulates, and two MZM connect the operating bias point of bias point controller (V1/V2) with control MZM respectively; Two ways of optical signals is input in the photoelectric detector respectively and detects up and down; The signal of setting out on a journey in this process is the main transmission path of effective RF signal; Following road signal is the linear compensation path; The signal of will setting out on a journey deducts down the road signal, promptly carries out electric territory difference processing, and the RF that can obtain suppressing through three rank receives signal

The scheme agent structure adopts single laser beam split to inject two MZM, independent light detection, electric territory difference processing mode.(two-way ratio 1 up and down: n), carrier signal was carried out beam splitting before getting into MZM, and power beam splitting ratio adopts n in two MZM, to import the RF signal of different amplitudes respectively ³: 1 mode (is n ³: the more powerful signal of 1 coupler output road output is connected with the MZM1 input; The MZM1 branch road is called sets out on a journey; Compensation road output of another output smaller power is connected with the input of MZM2, and the MZM2 branch road is called down road, makes carrier power among MZM1 and the MZM2 than being n ³: 1), in the RF signal that injects different amplitudes, can produce three onesize rank effects like this.Two-way is based on γ and sign relation are provided with condition of work as previously mentioned up and down.Under above-mentioned condition of work, can produce the identical third order intermodulation signal of amplitude; Carry out Photoelectric Detection and accomplish difference output through difference detector; Third order intermodulation signal that can amplitude is identical is cancelled out each other and is only kept the output of single order RF signal, realizes high linear transfer.

Scheme four basic functional principle

As shown in Figure 9; Concrete annexation is: among the MZM about the optical carrier with specific light power proportions relation of two laser outputs is injected in the two-way; The RF signal of while two-way specific amplitude ratio is input to the RF input of corresponding MZM and modulates, and two MZM connect the operating bias point of bias point controller (V1/V2) with control MZM respectively; Two ways of optical signals is input in the photoelectric detector respectively and detects up and down; The signal of setting out on a journey in this process is the main transmission path of effective RF signal; Following road signal is the linear compensation path; The signal of will setting out on a journey deducts down the road signal, promptly carries out electric territory difference processing, and the RF that can obtain suppressing through three rank receives signal.

The scheme agent structure adopts twin-laser to inject two MZM, independent light detection, electric territory difference processing mode respectively.(two-way ratio 1 up and down: n), the light carrier power proportions that gets into MZM adopts n in two MZM, to import the RF signal of different amplitudes respectively ³: (be that laser 1 is connected with linear modulator MZM1 input, laser 2 is connected with linear modulator MZM2 input 1 mode, and laser 1 is n with the power output ratio of laser 2 ³: 1), in the RF signal that injects different amplitudes, can produce three onesize rank effects like this.Two-way is based on γ and sign relation are provided with condition of work as previously mentioned up and down.Under above-mentioned condition of work, can produce the identical third order intermodulation signal of amplitude; Carry out Photoelectric Detection and accomplish difference output through difference detector; Third order intermodulation signal that can amplitude is identical is cancelled out each other and is only kept the output of single order RF signal, realizes high linear transfer.

Claims (12)

1. the third order intermodulation inhibition method of a linear transmission modulator the steps include:

1) carrier signal is input to respectively among two linear modulator MZM1, the MZM2, wherein, the carrier power among MZM1 and the MZM2 is than being n ³: 1;

2) radiofrequency signal RF is input to respectively among two linear modulator MZM1, the MZM2, wherein, the radiofrequency signal amplitude ratio of importing among MZM1 and the MZM2 is 1: n;

3) regulate two linear modulator MZM1, MZM2, make the light signal among MZM1, the MZM2 be orthogonal signalling each other, it is exported export after signal closes the road then;

Wherein, the radiofrequency signal RF phase place of importing in two linear modulators is opposite, or the quadrature bias point of working is different, or to adopt difference detector that the output signal is closed the radiofrequency signal RF phase place of importing in road output or the linear modulator opposite and work quadrature bias point is different and adopt difference detector that the output signal is closed road output;

Wherein, if MZM1 is n with the road ratio that closes that MZM2 exports signal ³: 1, then the n span is 1.8048～3.7045; If MZM1 is 1: 1 with the road ratio that closes of MZM2 output signal, then the n span is 1.5647～2.7686.

2. the method for claim 1 is characterized in that the MZM1 and the road ratio that closes of MZM2 output signal are n ³: 1 o'clock, the n span was 2.4286～2.5304; MZM1 is 1: 1 o'clock with the road ratio that closes of MZM2 output signal, and the n value is 2.

3. according to claim 1 or claim 2 method is characterized in that through a coupler 1 carrier signal being input to respectively among two linear modulator MZM1, the MZM2, and the splitting ratio of said coupler 1 is n ³: 1; Perhaps through two lasers carrier signal is input to respectively among two linear modulator MZM1, the MZM2, the power output of two-laser is than being n ³: 1.

4. according to claim 1 or claim 2 method, it is characterized in that making the light signal among MZM1, the MZM2 for the method for orthogonal signalling to be each other: the radiofrequency signal phase difference of regulating in two linear modulators is π n/2, n=± 1, ± 3, ± 5 Perhaps regulate the radiofrequency signal polarization angle difference δ in two linear modulators _Ploar=pi/2, or adopt independent light electro-detection path that road output is closed in output after the input.

5. a linear transmission modulator is characterized in that comprising a laser, and a splitting ratio is n ³: 1 coupler 1, two linear modulator MZM1, MZM2, a coupler 2, one phase shifters, a photoelectric detector; Said laser is connected with two said linear modulator MZM1, MZM2 input respectively through said coupler 1, makes carrier power among MZM1 and the MZM2 than being n ³: 1, said MZM1 signal output part closes the road input with one of said coupler 2 and is connected, and another closes the road input and is connected the signal output part of said MZM2 through said phase shifter and said coupler 2; Said coupler 2 outputs are connected with said photoelectric detector; Said phase shifter becomes differing of signal among MZM1, the MZM2 into 90 °; Wherein, the radiofrequency signal RF phase place of importing in two linear modulators is opposite, or the quadrature bias point of working different; The radiofrequency signal amplitude ratio of importing among MZM1 and the MZM2 is 1: n; If 2 couples of MZM1 of said coupler close the road than being n with MZM2 output signal ³: 1, then the n span is 1.8048～3.7045, if be 1: 1 to the road ratio that closes of MZM1 and MZM2 output signal, then the n span is 1.5647～2.7686.

6. linear transmission modulator as claimed in claim 5 is characterized in that the MZM1 and the road ratio that closes of MZM2 output signal are n ³: 1 o'clock, the n span was 2.4286～2.5304; MZM1 is 1: 1 o'clock with the road ratio that closes of MZM2 output signal, and the n value is 2.

7. a linear transmission modulator is characterized in that comprising a laser, and a splitting ratio is n ³: 1 coupler 1, two linear modulator MZM1, MZM2, a polarization mixer, a polarization rotator, a photoelectric detector; Said laser is connected with two said linear modulator MZM1, MZM2 input respectively through said coupler 1, makes carrier power among MZM1 and the MZM2 than being n ³: 1, said MZM1 signal output part closes the road input with one of said polarization mixer and is connected, and another closes the road input and is connected the signal output part of said MZM2 through said polarization rotator and said polarization mixer; Said polarization mixer output is connected with said photoelectric detector; Said polarization rotator is with the polarization state quadrature of signal among MZM1, the MZM2; Wherein, the radiofrequency signal RF phase place of importing in two linear modulators is opposite, or the quadrature bias point of working different; The radiofrequency signal amplitude ratio of importing among MZM1 and the MZM2 is 1: n; If said polarization mixer closes the road than being n to MZM1 and MZM2 output signal ³: 1, then the n span is 1.8048～3.7045, if be 1: 1 to the road ratio that closes of MZM1 and MZM2 output signal, then the n span is 1.5647～2.7686.

8. linear transmission modulator as claimed in claim 7 is characterized in that the MZM1 and the road ratio that closes of MZM2 output signal are n ³: 1 o'clock, the n span was 2.4286～2.5304; MZM1 is 1: 1 o'clock with the road ratio that closes of MZM2 output signal, and the n value is 2.

9. a linear transmission modulator is characterized in that comprising a laser, and a splitting ratio is n ³: 1 coupler 1, two linear modulator MZM1, MZM2, a difference detector; Said laser is connected with two said linear modulator MZM1, MZM2 input respectively through said coupler 1, makes carrier power among MZM1 and the MZM2 than being n ³: 1, said MZM1 signal output part is connected with a differential input end of said difference detector, and the signal output part of said MZM2 is connected with another differential input end of said difference detector; Wherein, the radiofrequency signal amplitude ratio of importing among MZM1 and the MZM2 is 1: n; Said difference detector is 1: 1 to MZM1 with the road ratio that closes that MZM2 exports signal, and the n span is 1.5647～2.7686.

10. linear transmission modulator as claimed in claim 9 is characterized in that the MZM1 and the road ratio that closes of MZM2 output signal are at 1: 1 o'clock, and the n value is 2.

11. a linear transmission modulator is characterized in that comprising two-laser 1,2, two linear modulator MZM1, MZM2, a difference detector; Said laser 1 is connected with said linear modulator MZM1 input; Said laser 2 is connected with said linear modulator MZM2 input; Said MZM1 signal output part is connected with a differential input end of said difference detector, and the signal output part of said MZM2 is connected with another differential input end of said difference detector; Wherein, laser 1 is n with the power output ratio of laser 2 ³: 1, the radiofrequency signal amplitude ratio of importing among MZM1 and the MZM2 is 1: n; Said difference detector is 1: 1 to MZM1 with the road ratio that closes that MZM2 exports signal, and the n span is 1.5647～2.7686.

12. linear transmission modulator as claimed in claim 9 is characterized in that the MZM1 and the road ratio that closes of MZM2 output signal are at 1: 1 o'clock, the n value is 2.

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