CN103401616B - A kind of radio frequency optical transmission system of high linearity and method - Google Patents

Abstract

The invention discloses a kind of radio frequency optical transmission system and method for high linearity, two parallel electro-optic phase modulator is adopted at transmitting terminal, two cover couplers and photoelectricity balanced detector is adopted to carry out relevant balance detection respectively to two-way modulation signal at receiving terminal, compared and RF signal voltage ratio by the light source power at transmitting terminal control inputs two parallel phase modulators, make two-way modulation signal equal by the power of the third order intermodulation component in the two path signal of relevant balance detection, adopt electric subtracter two path signal to be subtracted each other again and can offset third order intermodulation component, realize the suppression completely of third order intermodulation component, thus improve system linearity.Simultaneously owing to present invention employs relevant balance detection technology, the sensitivity of system can be improved, reduce relative intensity noise, thus reduce the noise factor of system.

Description

A kind of radio frequency optical transmission system of high linearity and method

Technical field

The invention belongs to radio frequency optical transport technology field, more specifically say, relate to a kind of radio frequency optical transmission system and method for high linearity.

Background technology

Radio frequency optical transmission system is that rf-signal modulation is loaded into light carrier, by recovering a kind of transmission system of radiofrequency signal after Optical Fiber Transmission in receiving terminal demodulation, is the important component part of frequency microwave communication system.In recent years, along with the develop rapidly of wireless communication technology, the application demand of radio frequency optical transmission system is also in growth by leaps and bounds.As a kind of applicability technology widely, radio frequency optical transmission system has important using value in commercial communication and national defense and military, its purposes covers radio communication, television broadcasting, radar fix, remote measuring and controlling, satellite communication, electronic warfare and entered the every field such as the cellular mobile communication equipment of average family completely now.

The dynamic range of radio frequency optical transmission system refers to the power bracket between the minimum signal that system can be transmitted and peak signal.It is subject to the restriction of two key factors: one is the noise of system, and two is the non-linear of system.In order to the radio frequency optical transmission system realizing great dynamic range just needs the system linear degree of lower system noise and Geng Gao.In radio frequency optical transmission system, the nonlinear most important nonlinear terms of influential system are third order intermodulation (Third-Order Intermodulation, IMD3) component.Therefore, the high linearity that realize system just means and will do better suppression to IMD3.

Research work based on the radio frequency optical transmission system of electro-optic intensity modulator has had the history of more than 30 year.The IMD3 suppression technology of this type systematic comprises pre-distortion technology, two intensity modulator parallel connections, series connection, and based on the mixed polarization states technology etc. of intensity modulator.At document [Dual Parallel ModulationSchemes for Low-Distortion Analog Optical Transmission, S.K.Korotky, R.M.DERidder, IEEE Photon.Technol.Lett.Vol.21, no.21, pp.1627-1629,2009.] in, author proposes the scheme of intensity modulator parallel connection, by regulating the luminous power and the RF signal voltage ratio that inject two modulators respectively, regulate 2 modulator direct current biasing points simultaneously, third-order non-linear amount distortion is inhibited.At document [Enhanced Spurious-Free Dynamic Range Using Mixed Polarization inOptical Single Sideband Mach-Zehnder Modulator, B.Masella, B.Hraimel, X.Zhang, J.Lightwave TechnoL, vol.27, no.15, pp.3034-3041, 2009.] in, author proposes the scheme of the mixed polarization states technology based on intensity modulator, different and the feature that modulation efficiency is different of polarization state in using degree modulator, by the effect regulating the polarized combination angle after injecting polarisation of light state and modulator to reach third-order non-linear distortion suppression.

But, because electro-optic intensity modulator itself exists inherent shortcoming, non-linear suppression based on the radio frequency optical transmission system of electro-optic intensity modulator has limitation, and electro-optic intensity modulator needs accurate feedback circuit to go to control DC offset voltage to control the transfer function of modulator.

Radio frequency optical transmission system based on electro-optic phase modulator becomes the research emphasis in this field in the last few years.The electrooptic modulation of electro-optic phase modulator be by rf-signal modulation in the phase place of light carrier, be a good linear process, there is not nonlinear distortion.But at receiving terminal, phase information being converted into strength information is non-linear process, still can bring nonlinear distortion to system.

Summary of the invention

The object of the invention is to overcome the deficiencies in the prior art, a kind of radio frequency optical transmission system and method for high linearity are provided, two parallel electro-optic phase modulator is adopted at transmitting terminal, by the suppression completely of power control realization third order intermodulation component, receiving terminal adopts relevant balance detection mode to receive, and improves sensitivity and the noise factor of system.

For achieving the above object, the radio frequency optical transmission system of high linearity of the present invention, comprise transmitting terminal, receiving terminal and optical fiber, it is characterized in that, described transmitting terminal comprises radiofrequency signal source module, radio-frequency power distribution module, light source module, the first electro-optic phase modulator, the second electro-optic phase modulator, described receiving terminal comprises local oscillator light source module, the first optical coupler, the second optical coupler, the first photoelectricity balanced detector, the second photoelectricity balanced detector, electric subtracter, wherein:

Radiofrequency signal source module, for generation of RF signal S _rF;

RF signal power distribution module, for the RF signal S produced by radiofrequency signal source module _rFbe divided into two-way RF signal S ₁(t) and S ₂t (), voltage is respectively V ₁and V ₂, by RF signal S ₁t () sends to the first electro-optic phase modulator, RF signal S ₂t () sends to the second electro-optic phase modulator;

Light source module, for generation of two LASER Light Source L ₁and L ₂, its frequency is identical, and power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, by light source L ₁send to the first electro-optic phase modulator, light source L ₂send to the second electro-optic phase modulator;

First electro-optic phase modulator, for by RF signal S ₁(t) and light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first coupler of receiving terminal is sent to by optical fiber;

Second electro-optic phase modulator, for by RF signal S ₂(t) and light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second coupler of receiving terminal is sent to by optical fiber;

Local oscillator light source module, for generation of two laser local oscillator light source L ' ₁with L ' ₂, local oscillator light source L ' ₁with light source L ₁relevant, local oscillator light source L ' ₂with light source L ₂relevant, by local oscillator light source L ' ₁send to the first coupler, local oscillator light source L ' ₂send to the second coupler;

First optical coupler, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first photoelectricity balanced detector;

Second optical coupler, for will with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second photoelectricity balanced detector;

First photoelectricity balanced detector, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter;

Second photoelectricity balanced detector, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter;

Electricity subtracter, for being subtracted each other by two signals of telecommunication, be restored RF signal S

The present invention also provides a kind of radio frequency optical transmission method of the radio frequency optical transmission system based on high linearity, it is characterized in that, comprising:

S1: transmitting terminal is by RF signal S _rFbe divided into two-way RF signal S ₁(t) and S ₂t (), voltage is respectively V ₁and V ₂, use two LASER Light Source L respectively ₁and L ₂radio frequency signal S ₁(t) and S ₂t () carries out electric light phase-modulation, the power of two LASER Light Source is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, after electric light phase-modulation, obtain two paths of signals light X ₁and X ₂and by fibre optical transmission to receiving terminal;

S2: receiving terminal Received signal strength light X ₁and X ₂, adopt two laser local oscillator light source L ' respectively ₁with L ' ₂to flashlight X ₁and X ₂carry out coupling to be concerned with, then the two paths of signals Y that will obtain ₁and Y ₂carry out photoelectricity balance and detect two path signal T ₁, T ₂, two path signal is subtracted each other, the radiofrequency signal be restored

The radio frequency optical transmission system of high linearity of the present invention and method, two parallel electro-optic phase modulator is adopted at transmitting terminal, two cover couplers and photoelectricity balanced detector is adopted to carry out relevant balance detection respectively to two paths of signals light at receiving terminal, in the light source power ratio of transmitting terminal control inputs two parallel phase modulators and the relation of RF signal voltage ratio, make two paths of signals light equal by the power of the third order intermodulation component in the two path signal of relevant balance detection, adopt electric subtracter two path signal to be subtracted each other again and can offset third order intermodulation component, realize the suppression completely of third order intermodulation component, thus improve system linearity.Simultaneously owing to present invention employs relevant balance detection technology, the sensitivity of system can be improved, reduce relative intensity noise, thus reduce the noise factor of system.

Accompanying drawing explanation

Fig. 1 is a kind of embodiment structure chart of the radio frequency optical transmission system of high linearity of the present invention;

Fig. 2 is the schematic diagram of photoelectricity balance detection in the present invention;

Fig. 3 is the structural representation of the embodiment of the present invention 1;

Fig. 4 is the structural representation of the embodiment of the present invention 2;

Fig. 5 is the structural representation of the embodiment of the present invention 3;

Fig. 6 is the signal of telecommunication spectrum results that during embodiment 2 emulates, the first balanced detector exports;

Fig. 7 is the signal of telecommunication spectrum results that during embodiment 2 emulates, the second balanced detector exports;

Fig. 8 is the signal of telecommunication spectrum results that during embodiment 2 emulates, electric subtracter exports.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in and will be left in the basket here.

Fig. 1 is a kind of embodiment structure chart of the radio frequency optical transmission system of high linearity of the present invention.As shown in Figure 1, the present invention includes transmitting terminal, receiving terminal and optical fiber, wherein transmitting terminal comprises radiofrequency signal source module 5, radio-frequency power distribution module 4, light source module 1, first electro-optic phase modulator 2, second electro-optic phase modulator 3, described receiving terminal comprises local oscillator light source module 6, first optical coupler 7, second optical coupler 8, first photoelectricity balanced detector 9, second photoelectricity balanced detector 10, electric subtracter 11, wherein:

Radiofrequency signal source module 5, for generation of RF signal S _rF.

RF signal power distribution module 4, for the RF signal S produced by radiofrequency signal source module 5 _rFbe divided into two-way RF signal S ₁and S ₂, voltage is respectively V ₁and V ₂, by RF signal S ₁send to the first electro-optic phase modulator 2, RF signal S ₂send to the second electro-optic phase modulator 3.

Light source module 1, for generation of two LASER Light Source L ₁and L ₂, its frequency is identical, and power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, by light source L ₁send to the first electro-optic phase modulator 2, light source L ₂send to the second electro-optic phase modulator 3.Light source module 1 can adopt the composite module of a laser and a beam splitter.

First electro-optic phase modulator 2, for by RF signal S ₁with light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first optical coupler 7 of receiving terminal is sent to by optical fiber.

Second electro-optic phase modulator 3, for by RF signal S ₂with light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second optical coupler 8 of receiving terminal is sent to by optical fiber.

Local oscillator light source module 6, for generation of two laser local oscillator light source L ' ₁with L ' ₂, local oscillator light source L ' ₁with light source L ₁relevant, local oscillator light source L ' ₂with light source L ₂relevant, by local oscillator light source L ' ₁send to the first optical coupler 7, local oscillator light source L ' ₂send to the second optical coupler 8.

First optical coupler 7, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first balanced detector 9.

Second optical coupler 8, for by flashlight X ₂with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second balanced detector 10;

First photoelectricity balanced detector 9, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter 11;

Second photoelectricity balanced detector 10, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter 11;

Electricity subtracter 11, for being subtracted each other by two signals of telecommunication, be restored radiofrequency signal

The present invention also provides a kind of radio frequency optical transmission method of the radio frequency optical transmission system based on high linearity, it is characterized in that, comprising:

S1: transmitting terminal is by RF signal S _rFbe divided into two-way RF signal S ₁(t) and S ₂t (), voltage is respectively V ₁and V ₂, use two LASER Light Source L respectively ₁and L ₂radio frequency signal S ₁(t) and S ₂t () carries out electric light phase-modulation, the power of two LASER Light Source is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, after electric light phase-modulation, obtain two paths of signals light X ₁and X ₂and by fibre optical transmission to receiving terminal;

S2: receiving terminal Received signal strength light X ₁and X ₂, adopt two laser local oscillator light source L ' respectively ₁with L ' ₂to flashlight X ₁and X ₂carry out coupling to be concerned with, then the two paths of signals Y that will obtain ₁and Y ₂carry out photoelectricity balance and detect two path signal T ₁, T ₂, two path signal is subtracted each other, the radiofrequency signal be restored

The present invention, at transmitting terminal, have employed two parallel electro-optic phase modulator, and adopt relevant balance detection at receiving terminal, the power stage of the third order intermodulation component of two photoelectricity balanced detector can be expressed as follows:

$P_{3\mathrm{th}1}=\frac{1}{128}{P_1}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

$P_{3\mathrm{th}2}=\frac{1}{128}{P_2}^2{V_2}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Wherein P ₁and P ₂represent the input optical power of two electro-optic phase modulators and the input optical power of two optical couplers respectively, V ₁and V ₂for inputting the RF signal voltage size of two electro-optic phase modulators respectively, r _dfor the photoelectric conversion efficiency of photoelectricity balanced detector, α represents the insertion loss of electro-optic phase modulator, V _πrepresent the half-wave voltage of electro-optic phase modulator, Z _outrepresent the output impedance of photoelectricity balanced detector.

Can find from above formula, when conservative control optical output power of laser than and RF signal voltage than time, i.e. P ₁/ P ₂=(V ₂/ V ₁) ³, then at receiving terminal, two paths of signals can be subtracted each other, third order intermodulation distortion can be made to be cancelled completely, thus the suppression of good third-order non-linear distortion can be reached, achieve the expansion of dynamic range.

The present invention, at receiving terminal, have employed relevant balance detection mode.Coherent detection is a kind of detection mode conventional at present, and the power output of coherent detection is: P _coherent=2a ²p _sp _lr _l, and the power output of traditional direct detection is: P _directly=a ²p _s ²r _l, wherein be respectively the average power of flashlight and local oscillator light, R _lfor load resistance.Usual P _l> P _s, therefore coherent detection can provide sufficiently high gain, effective especially to infant laser signal detection.

Balance detection is a kind of technology occurred along with the development of coherent detection technology, and its Main Function is used to the noise reducing local laser, is widely used in microwave light link field.Fig. 2 is the schematic diagram of photoelectricity balance detection in the present invention.As shown in Figure 2, flashlight E ₁(t) and local oscillator light E ₂t (), after coupler is relevant, obtains the signal after being coupled, comprises E ₃(t) and E ₄t () two-way, input photoelectricity balanced detector, photoelectricity balanced detector can be equivalent to two photodetectors and an electric subtracter, and two detectors are respectively to E ₃(t) and E ₄t () carries out photodetection, obtain two signal of telecommunication i ₁(t) and i ₂t (), electric subtracter subtracts each other two signals of telecommunication and obtains signal of telecommunication i (t)=i ₁(t)-i ₂(t).

Balanced detector in radio frequency optical transmission system of the present invention uses two photodetectors, and because shot noise is difference mode signal, so the shot noise introduced is more than using the system of single detector.But the relative intensity noise of laser is common-mode signal, so balance detection can reduce the relative intensity noise of system, if the relative intensity noise that can offset is greater than the shot noise of increase, then the noise decrease of whole system, noise factor can reduce.

Embodiment 1

Fig. 3 is the structural representation of the embodiment of the present invention 1.As shown in Figure 3, in the present embodiment, at transmitting terminal, radiofrequency signal source module 5 produces two angular frequencies and is respectively ω ₁and ω ₂sine wave signal, two sine wave signals are combined into a road by electric coupling and export RF signal power distribution module to.

RF signal power distribution module 4 comprises the 3rd beam splitter 401 and electrical attenuator 402, wherein:

Electricity beam splitter 401, for the RF signal S produced by radiofrequency signal source module 5 _rFbe divided into two-way RF signal S ₁(t) and S ₂(t).

Electrical attenuator 402, for regulating RF signal S ₁(t) or S ₂the power of (t).In the present embodiment, for changing RF signal S ₂the power of (t).

For the ease of the power division of light source, the power of two-way radiofrequency signal is usually made to meet predetermined power ratio when RF signal power distributes.In the present embodiment, RF signal S is set ₁t the voltage of () is V ₁, RF signal S ₂voltage be V ₂, then the RF signal S of the first electro-optic phase modulator 2 is inputted ₁the RF signal S of (t) and input the second electro-optic phase modulator 3 ₂t the expression formula of () is respectively:

S ₁(t)=V ₁(sin(ω ₁t)+sin(ω ₂t))，

S ₂(t)=V ₂(sin(ω ₁t)+sin(ω ₂t))。

In the present embodiment, light source module 1 adopts a laser generation light source to carry out beam splitting, comprises laser 101, first amplifier 102, first Polarization Controller 103, first beam splitter 104.

Laser 101, for generation of a road LASER Light Source.

First amplifier 102, amplifies for the light source produced laser 101.The effect of the first amplifier 102 is the power in order to control light source better.

First Polarization Controller 103, for regulating the polarization state of light source, the light source amplified by the first amplifier 102 carries out polarization adjustment.In light source module 1, configure Polarization Controller 103 mainly in order to determine the polarization state of light source, the flashlight that the polarization state that the local oscillator light source module 6 being convenient to receiving terminal controls local oscillator light source makes local oscillator light source and receiving terminal receive is concerned with.

First beam splitter 104, for being divided into two-beam source L by light source ₁and L ₂, power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³.Two-beam source L ₁and L ₂send to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively.

Two-beam source L ₁and L ₂luminous intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_1}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

$E_2=\frac{\sqrt{P_2}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

Wherein, i is imaginary unit, ω ₀for the angular frequency of light source.

First electro-optic phase modulator 2, for by RF signal S ₁(t) and light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first coupler 7 of receiving terminal is sent to by optical fiber 12.

Second electro-optic phase modulator 3, for by RF signal S ₂(t) and light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second coupler 8 of receiving terminal is sent to by optical fiber 12.

The distribution of light intensity expression formula of two electro-optic phase modulator output signal light is respectively:

$E_{\mathrm{PM}1}=\frac{\sqrt{P_1}}{2}\exp [{\mathrm{i\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_1\left(t\right)]$

$E_{\mathrm{PM}2}=\frac{\sqrt{P_2}}{2}\exp [i{\mathrm{\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_2\left(t\right)]$

Wherein, V _πrepresent the half-wave voltage of electro-optic phase modulator, in two electro-optic phase modulators, this parameter is consistent.

At receiving terminal, in the present embodiment, local oscillator light source module 6 adopts a local oscillator laser generation laser local oscillator light source to carry out beam splitting, comprises local oscillator laser 601, second amplifier 602, second Polarization Controller 603, second beam splitter 604, wherein:

Local oscillator laser 601, for generation of the laser local oscillator light source that a road frequency and the direction of propagation are all identical with light source.The frequency of local oscillator light source is identical with the direction of propagation and light source, is to enable local oscillator light source be concerned with the flashlight obtained through rf-signal modulation.

Second amplifier 602, amplifies for the local oscillator light source produced by local oscillator laser 601.The effect of the second amplifier 102 is the power in order to control local oscillator light source better.

Second Polarization Controller 603, for modulating the polarization state of local oscillator light source, the flashlight polarization direction that itself and receiving terminal are received is identical.Local oscillator light source is identical with the polarization direction of flashlight is also to ensure that local oscillator light source can be concerned with the flashlight obtained through rf-signal modulation.If in Optical Fiber Transmission process, the polarization state of flashlight does not change, then the polarization direction of flashlight that receives of receiving terminal is identical with the polarization direction of light source used during rf-signal modulation, then when the polarization state that the second Polarization Controller 603 carries out local oscillator light source regulates, directly can contrast the polarization state of the light source that light source module produces.Therefore, the optical fiber 12 in the present invention can adopt polarization maintaining optical fibre.

Second beam splitter 604, for being divided into two bundle local oscillator light source L ' by the local oscillator light source regulated through the second Polarization Controller 603 ₁with L ' ₂.Two bundle local oscillator light source L ' ₁with L ' ₂send to the first optical coupler 7 and the second optical coupler 8 respectively.In the present embodiment, local oscillator light source L ' ₁with L ' ₂with corresponding light source L ₁and L ₂power identical.

Two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_1}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right),$

$E_2=\frac{\sqrt{P_2}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right).$

Visible, in the present embodiment, two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity consistent with light source.

First optical coupler 7, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first photoelectricity balanced detector 9.

Second optical coupler 8, for by flashlight X ₂with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second photoelectricity balanced detector 10.

First photoelectricity balanced detector 9, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter 11.Signal of telecommunication T ₁middle fundamental component power expression is:

$P_{\mathrm{RF}1}=\frac{1}{2}{P_1}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}1}=\frac{1}{128}{P_1}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Second photoelectricity balanced detector 10, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter 11.Signal of telecommunication T ₂middle fundamental component power expression is:

$P_{\mathrm{RF}2}=\frac{1}{2}{P_2}^2{V_2}^2{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}2}=\frac{1}{128}{P_2}^2{V_2}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Electricity subtracter 11, for being subtracted each other by two signals of telecommunication, be restored radiofrequency signal visible, due to P in the present invention ₁/ P ₂=(V ₂/ V ₁) ³, subtracted each other by two signals of telecommunication by electric subtracter 11, third order intermodulation component is completely suppressed, final recovery radiofrequency signal the only output of remaining fundamental frequency signal:

$P_{\mathrm{RF}}=\frac{1}{2}({P_1}^2{V_1}^2-{P_2}^2{V_2}^2){r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}.$

Embodiment 2

Fig. 4 is the structural representation of the embodiment of the present invention 2.As shown in Figure 4, in the present embodiment, except light source module 1 and local oscillator light source module 6, other modules are identical with embodiment 1.

Radiofrequency signal source module 5 is consistent with embodiment 1, produces two angular frequencies and is respectively ω ₁and ω ₂sine wave signal, two sine wave signals are combined into a road by electric coupling and export RF signal power distribution module 4 to.

RF signal power distribution module 4 comprises the RF signal S of the 3rd beam splitter 401 and the generation of electrical attenuator 402 radio frequency signal source module 5 _rFcarry out beam splitting and power adjustments, similarly, in the present embodiment, RF signal S is set ₁t the voltage of () is V ₁, RF signal S ₂voltage be V ₂, then the RF signal S of the first electro-optic phase modulator 2 is inputted ₁the RF signal S of (t) and input the second electro-optic phase modulator 3 ₂t the expression formula of () is respectively:

S ₁(t)=V ₁(sin(ω ₁t)+sin(ω ₂t))，

S ₂(t)=V ₂(sin(ω ₁t)+sin(ω ₂t))。

In the present embodiment, light source module 1, except laser 101, first amplifier 102, first Polarization Controller 103, first beam splitter 104, also comprises the 3rd beam splitter 105, the light source beam splitting produced by laser 101.The light source that laser 101 produces is divided into two bundles by the 3rd beam splitter 105, is wherein a branch ofly used for signal phase modulation as light source, a branch ofly in addition sends to the local oscillator light source module of receiving terminal as local oscillator light source by optical fiber.In the present embodiment, the light source that the 3rd beam splitter 105 beam splitting obtains is two bundles, a branch ofly sends to the first amplifier 102 as light source, a branch of local oscillator light source module 6 being sent to receiving terminal by optical fiber 12 in addition.In the present embodiment, the two-beam source power that the 3rd beam splitter 105 beam splitting obtains is identical.

In light source module 1, the light source that the 3rd beam splitter 105 obtains amplifies by the first amplifier 102.

First Polarization Controller 103, for regulating the polarization state of light source, the light source amplified by the first amplifier 102 carries out polarization adjustment.

First beam splitter 104, for being divided into two-beam source L by the light source regulated through Polarization Controller 103 ₁and L ₂, power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³.Two-beam source L ₁and L ₂send to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively.

Similarly, two-beam source L ₁and L ₂luminous intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_1}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

$E_2=\frac{\sqrt{P_2}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

Wherein, i is imaginary unit, ω ₀for the angular frequency of light source.

First electro-optic phase modulator 2, for by RF signal S ₁(t) and light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first coupler 7 of receiving terminal is sent to by optical fiber 12.

Second electro-optic phase modulator 3, for by RF signal S ₂(t) and light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second coupler 8 of receiving terminal is sent to by optical fiber 12.

The distribution of light intensity expression formula of two electro-optic phase modulator output signal light is respectively:

$E_{\mathrm{PM}1}=\frac{\sqrt{P_1}}{2}\exp [{\mathrm{i\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_1\left(t\right)]$

$E_{\mathrm{PM}2}=\frac{\sqrt{P_2}}{2}\exp [i{\mathrm{\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_2\left(t\right)]$

Wherein, V _πrepresent the half-wave voltage of electro-optic phase modulator, in two electro-optic phase modulators, this parameter is consistent.

In the present embodiment, because the light source module 1 of local oscillator light source by transmitting terminal produces, therefore do not need configuration local oscillator laser in local oscillator light source module 6, local oscillator light source module 6 comprises the second amplifier 602, second Polarization Controller 603 and the second beam splitter 604, wherein:

Second amplifier 602, for amplifying the local oscillator received from light source module 1 light source.

Second Polarization Controller 603, for modulating the polarization state of local oscillator light source, the flashlight polarization direction that itself and receiving terminal are received is identical.Similarly, when optical fiber 12 adopts polarization maintaining optical fibre, the polarization state of the flashlight that receiving terminal receives is consistent with light source used during phase-modulation, and the second Polarization Controller 603 directly contrasts the polarization state of light source when the polarization state of carrying out local oscillator light source regulates.

Second beam splitter 604, for being divided into two bundle local oscillator light source L ' by the local oscillator light source regulated through the second Polarization Controller 603 ₁with L ' ₂.Two bundle local oscillator light source L ' ₁with L ' ₂send to the first optical coupler 7 and the second optical coupler 8 respectively.In the present embodiment, local oscillator light source L ' ₁with L ' ₂with corresponding light source L ₁and L ₂power identical.

Two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_1}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right),$

$E_2=\frac{\sqrt{P_2}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right).$

Visible, in the present embodiment, two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity consistent with light source.

First optical coupler 7, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first photoelectricity balanced detector 9.

Second optical coupler 8, for by flashlight X ₂with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second photoelectricity balanced detector 10.

First photoelectricity balanced detector 9, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter 11.Signal of telecommunication T ₁middle fundamental component power expression is:

$P_{\mathrm{RF}1}=\frac{1}{2}{P_1}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}1}=\frac{1}{128}{P_1}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Second photoelectricity balanced detector 10, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter 11.Signal of telecommunication T ₂middle fundamental component power expression is:

$P_{\mathrm{RF}2}=\frac{1}{2}{P_2}^2{V_2}^2{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}2}=\frac{1}{128}{P_2}^2{V_2}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Electricity subtracter 11, for being subtracted each other by two signals of telecommunication, be restored radiofrequency signal

Identical with embodiment 1, due to P ₁/ P ₂=(V ₂/ V ₁) ³, subtracted each other by the signal of telecommunication that two photoelectricity balanced detector obtain eventually through electric subtracter 11, third order intermodulation component is completely suppressed, final recovery radiofrequency signal the only output of remaining fundamental frequency signal:

$P_{\mathrm{RF}}=\frac{1}{2}({P_1}^2{V_1}^2-{P_2}^2{V_2}^2){r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}.$

Embodiment 3

Fig. 5 is the structural representation of the embodiment of the present invention 3.As shown in Figure 5, in the present embodiment, except light source module 1 and local oscillator light source module 6, other modules are identical with embodiment 1.

At transmitting terminal, radiofrequency signal source module 5 in the same manner as in Example 1, produces two angular frequencies and is respectively ω ₁and ω ₂sine wave signal, two sine wave signals are combined into a road by electric coupling and export RF signal power distribution module to.

RF signal power distribution module 4 comprises the RF signal S of the 3rd beam splitter 401 and the generation of electrical attenuator 402 radio frequency signal source module 5 _rFcarry out beam splitting and power adjustments, similarly, in the present embodiment, RF signal S is set ₁t the voltage of () is V ₁, RF signal S ₂voltage be V ₂, then the RF signal S of the first electro-optic phase modulator 2 is inputted ₁the RF signal S of (t) and input the second electro-optic phase modulator 3 ₂t the expression formula of () is respectively:

S ₁(t)=V ₁(sin(ω ₁t)+sin(ω ₂t))，

S ₂(t)=V ₂(sin(ω ₁t)+sin(ω ₂t))。

In the present embodiment, light source module 1 adopts a laser generation light source to carry out beam splitting, comprises laser 101, first amplifier 102, first Polarization Controller 103, first polarization beam apparatus 105.

Laser 101, for generation of a road LASER Light Source.

First amplifier 102, amplifies for the light source produced laser 101.The effect of the first amplifier 102 is the power in order to control light source better.

First Polarization Controller 103, for regulating the polarization state of light source, the light source amplified by the first amplifier 102 carries out polarization adjustment.In the present embodiment, it is the power division of being convenient to carry out local oscillator light source in local oscillator light source module 6 that the first Polarization Controller 103 pairs light source carries out polarization state adjustment.

First polarization beam apparatus 105, for by the two-way orthogonal polarisation state of optical device to polarization beam apparatus 105, is divided into two-beam source L ₁and L ₂, power is respectively P _xand P _y, and its power ratio P _x/ P _y=(V ₂/ V ₁) ³.Two-beam source L ₁and L ₂send to the first electro-optic phase modulator 2 and the second electro-optic phase modulator 3 respectively.In embodiment 1 and 2, light source L ₁and L ₂polarization state is identical, in the present embodiment, and light source L ₁and L ₂polarization state is orthogonal.

Two-beam source L ₁and L ₂luminous intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_x}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

$E_2=\frac{\sqrt{P_y}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right)$

Wherein, i is imaginary unit, ω ₀for the angular frequency of light source.

First electro-optic phase modulator 2, for by RF signal S ₁(t) and light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first coupler 7 of receiving terminal is sent to by optical fiber 12.

Second electro-optic phase modulator 3, for by RF signal S ₂(t) and light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second coupler 8 of receiving terminal is sent to by optical fiber 12.

The distribution of light intensity expression formula of two electro-optic phase modulator output signal light is respectively:

$E_{\mathrm{PM}1}=\frac{\sqrt{P_x}}{2}\exp [{\mathrm{i\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_1\left(t\right)]$

$E_{\mathrm{PM}2}=\frac{\sqrt{P_y}}{2}\exp [i{\mathrm{\ω}}_{0}t+i\frac{\mathrm{\π}}{V_{\mathrm{\π}}}{S}_2\left(t\right)]$

Wherein, V _πrepresent the half-wave voltage of electro-optic phase modulator, in two electro-optic phase modulators, this parameter is consistent.

At receiving terminal, in the present embodiment, local oscillator light source module 6 adopts a local oscillator laser generation laser local oscillator light source to carry out beam splitting, comprises local oscillator laser 601, second amplifier 602, second Polarization Controller 603, polarization beam apparatus 605, wherein:

Local oscillator laser 601, for generation of the laser local oscillator light source that a road frequency and the direction of propagation are all identical with light source.

Second amplifier 602, amplifies for the local oscillator light source produced by local oscillator laser 601.

Second Polarization Controller 603, for modulating the polarization state of local oscillator light source, makes it identical with light source polarization direction, is convenient to the power division that the second polarization beam apparatus 604 carries out local oscillator light source.

Second polarization beam apparatus 604, for being divided into two bundle local oscillator light source L ' by the local oscillator light source regulated through the second Polarization Controller 603 ₁with L ' ₂.Two bundle local oscillator light source L ' ₁with L ' ₂send to the first optical coupler 7 and the second optical coupler 8 respectively.In the present embodiment, local oscillator light source L ' ₁with L ' ₂with corresponding light source L ₁and L ₂power identical.

Two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity expression formula be respectively:

$E_1=\frac{\sqrt{P_x}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right),$

$E_2=\frac{\sqrt{P_y}}{2}\exp \left(i{\mathrm{\ω}}_{0}t\right).$

Visible, in the present embodiment, two bundle local oscillator light source L ' ₁with L ' ₂distribution of light intensity consistent with light source.

First optical coupler 7, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first photoelectricity balanced detector 9.

Second optical coupler 8, for by flashlight X ₂with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second photoelectricity balanced detector 10.

First photoelectricity balanced detector 9, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter 11.Signal of telecommunication T ₁middle fundamental component power expression is:

$P_{\mathrm{RF}1}=\frac{1}{2}{P_x}^2{V_1}^2{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}1}=\frac{1}{128}{P_x}^2{V_1}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Second photoelectricity balanced detector 10, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter 11.Signal of telecommunication T ₂middle fundamental component power expression is:

$P_{\mathrm{RF}2}=\frac{1}{2}{P_y}^2{V_2}^2{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}$

Third order intermodulation component power is:

$P_{3\mathrm{th}2}=\frac{1}{128}{P_y}^2{V_2}^6{r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^6{Z}_{\mathrm{out}}$

Electricity subtracter 11, for being subtracted each other by two signals of telecommunication, be restored radiofrequency signal visible, due to P in the present embodiment _x/ P _y=(V ₂/ V ₁) ³, subtracted each other by two signals of telecommunication by electric subtracter 11, third order intermodulation component is completely suppressed, final recovery radiofrequency signal the only output of remaining fundamental frequency signal:

$P_{\mathrm{RF}}=\frac{1}{2}({P_x}^2{V_1}^2-{P_y}^2{V_2}^2){r_d}^2{\mathrm{\α}}^2\·{\left(\frac{\mathrm{\π}}{V_{\mathrm{\π}}}\right)}^2{Z}_{\mathrm{out}}.$

Embodiment 2 is adopted to emulate.Simulation parameter is: P ₁=90mw, P ₂=10mw, V ₁=0.2V, V ₂=0.42V, ω ₁=10GHz, ω ₂=12GHz, r _d=1.0A/W.Fig. 6 is the signal of telecommunication spectrum results that during embodiment 2 emulates, the first balanced detector exports.Fig. 7 is the signal of telecommunication spectrum results that during embodiment 2 emulates, the second balanced detector exports.Fig. 8 is the signal of telecommunication spectrum results that in embodiment 2, electric subtracter exports.As shown in Figure 6 to 8, the light adopting radio frequency optical transmission system of the present invention to carry out radiofrequency signal carries transmission, and third order intermodulation component is almost totally constrained, and the loss of fundamental frequency signal is very little, thus system linearity degree is improved, and dynamic range also increases thereupon.

Although be described the illustrative embodiment of the present invention above; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.

Claims (10)

1. the radio frequency optical transmission system of a high linearity, comprise transmitting terminal, receiving terminal and optical fiber, it is characterized in that, described transmitting terminal comprises radiofrequency signal source module, radio-frequency power distribution module, light source module, the first electro-optic phase modulator, the second electro-optic phase modulator, described receiving terminal comprises local oscillator light source module, the first optical coupler, the second optical coupler, the first photoelectricity balanced detector, the second photoelectricity balanced detector, electric subtracter, wherein:

Radiofrequency signal source module, for generation of RF signal S _rF;

RF signal power distribution module, for the RF signal S produced by radiofrequency signal source module _rFbe divided into two-way RF signal S ₁(t) and S ₂t (), voltage is respectively V ₁and V ₂, by RF signal S ₁t () sends to the first electro-optic phase modulator, RF signal S ₂t () sends to the second electro-optic phase modulator;

Light source module, for generation of two LASER Light Source L ₁and L ₂, its frequency is identical, and power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, by light source L ₁send to the first electro-optic phase modulator, light source L ₂send to the second electro-optic phase modulator;

First electro-optic phase modulator, for by RF signal S ₁(t) and light source L ₁carry out phase-modulation, the flashlight X obtained ₁the first coupler of receiving terminal is sent to by optical fiber;

Second electro-optic phase modulator, for by RF signal S ₂(t) and light source L ₂carry out phase-modulation, the flashlight X obtained ₂the second coupler of receiving terminal is sent to by optical fiber;

Local oscillator light source module, for generation of two laser local oscillator light source L ' ₁with L ' ₂, local oscillator light source L ' ₁with light source L ₁relevant, local oscillator light source L ' ₂with light source L ₂relevant, by local oscillator light source L ' ₁send to the first coupler, local oscillator light source L ' ₂send to the second coupler;

First optical coupler, for by flashlight X ₁with local oscillator light source L ' ₁be coupled, by the signal Y after coupling ₁send to the first photoelectricity balanced detector;

Second optical coupler, for by flashlight X ₂with local oscillator light source L ' ₂be coupled, by the signal Y after coupling ₂send to the second photoelectricity balanced detector;

First photoelectricity balanced detector, for by signal Y ₁be converted into signal of telecommunication T ₁, send to electric subtracter;

Second photoelectricity balanced detector, for by signal Y ₂be converted into signal of telecommunication T ₂, send to electric subtracter;

Electricity subtracter, for being subtracted each other by two signals of telecommunication, be restored radiofrequency signal

2. radio frequency optical transmission system according to claim 1, is characterized in that, described RF signal power distribution module comprises electric beam splitter and electrical attenuator, wherein:

Electricity beam splitter, for the RF signal S produced by radiofrequency signal source module _rFbe divided into two-way RF signal S ₁(t) and S ₂(t);

Electrical attenuator, for regulating RF signal S ₁(t) or S ₂the power of (t).

3. radio frequency optical transmission system according to claim 1, is characterized in that, described light source module comprises laser and the first beam splitter, wherein:

Laser, for generation of a road LASER Light Source;

First beam splitter, for being divided into two-beam source L by light source ₁and L ₂, power is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³.

4. radio frequency optical transmission system according to claim 3, is characterized in that, described light source module also comprises the first Polarization Controller, is connected with the first beam splitter, the polarization state of the light source produced for regulating laser.

5. radio frequency optical transmission system according to claim 3, is characterized in that, described first beam splitter is polarization beam apparatus.

6. radio frequency optical transmission system according to claim 3, it is characterized in that, described light source module also comprises the 3rd beam splitter, by the light source beam splitting that laser produces, wherein a branch of as light source, a branch ofly in addition sends to the local oscillator light source module of receiving terminal as local oscillator light source by optical fiber.

7. radio frequency optical transmission system according to claim 1, is characterized in that, described local oscillator light source module comprises local oscillator laser, the second Polarization Controller and the second beam splitter, wherein:

Local oscillator laser, for generation of the laser local oscillator light source that a road frequency and the direction of propagation are all identical with light source;

Second beam splitter, for being divided into two bundle local oscillator light source L ' by the local oscillator light source regulated through the second Polarization Controller ₁with L ' ₂;

Second Polarization Controller, is connected with the second beam splitter, the polarization state of the local oscillator light source produced for regulating local oscillator laser.

8. radio frequency optical transmission system according to claim 7, is characterized in that, described second beam splitter is polarization beam apparatus.

9., according to the arbitrary described radio frequency optical transmission system of claim 1 to 8, it is characterized in that, described optical fiber is polarization maintaining optical fibre.

10. a radio frequency optical transmission method for high linearity, is characterized in that, comprise the following steps:

S1: transmitting terminal is by RF signal S _rFbe divided into two-way RF signal S ₁(t) and S ₂t (), voltage is respectively V ₁and V ₂, use two LASER Light Source L respectively ₁and L ₂radio frequency signal S ₁(t) and S ₂t () carries out electric light phase-modulation, the power of two LASER Light Source is respectively P ₁and P ₂, and its power ratio P ₁/ P ₂=(V ₂/ V ₁) ³, after electric light phase-modulation, obtain two paths of signals light X ₁and X ₂and by fibre optical transmission to receiving terminal;

S2: receiving terminal Received signal strength light X ₁and X ₂, adopt two laser local oscillator light source L ' respectively ₁with L ' ₂to flashlight X ₁and X ₂carry out coupling to be concerned with, then the two paths of signals Y that will obtain ₁and Y ₂carry out photoelectricity balance respectively and detect two path signal T ₁, T ₂, two path signal is subtracted each other, the radiofrequency signal be restored